Mitsubishi Air Conditioner: Complete Troubleshooting Guide


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Mitsubishi air conditioners are some of the best ACs around. However, even the best air conditioner will malfunction at some point, and Mitsubishi ACs are no exception.

That’s why I’ve put together this complete Mitsubishi air conditioner troubleshooting guide. I’ve put together step-by-step instructions on how to identify and fix every issue your Mitsubishi AC might experience. I’ll also tell you when an issue is complicated that you should call an HVAC repair service instead of trying to fix it yourself.

Let’s get to it. This is a large guide, so I recommend that you use this table of contents to quickly jump to the issue your AC is experiencing:

Mitsubishi Air Conditioner Not Heating/Not Blowing Hot Air

A Mitsubishi AC that’s not heating has a wrong operation mode setting or higher room temperature than the set temperature. Also, the Heat mode may not have taken effect yet or the AC is too small for the space. A wrong mode setting is the most common cause. Simply set the AC on the Heat/Auto mode.

Wrong Mitsubishi AC Mode Setting/High Room Temperature

If your Mitsubishi AC model allows you to switch between cooling and heating, you will need to set it on the HEAT mode for it to blow hot air. You can also set it on the AUTO mode, which allows your AC to switch mode according to room temperature.

On the HEAT mode, your Mitsubishi AC will blow warm air until the set temperature is attained. After that, the compressor will switch off gradually then restart again when the room temperature falls below the set temperature.

On the AUTO mode, your Mitsubishi AC will switch from COOL to HEAT mode depending on the temperature: switch to COOL mode if the room temperature is 2 degrees higher than the set temperature for 15 minutes and switch to HEAT mode if the room temperature is 2 degrees lower than the set temperature for 15 minutes.

How to Diagnose Wrong Mitsubishi AC Mode Setting

Check to ensure that your Mitsubishi AC is set on either the HEAT or AUTO mode and not the COOL or DRY mode.

How to Fix Wrong Mitsubishi AC Mode Setting/High Room Temperature

If your Mitsubishi AC is not heating but it’s set on the COOL or DRY mode, use the AC’s remote control to select the HEAT or AUTO mode by pressing the MODE button until the desired mode is displayed. The Mode operation changes from AUTO → COOL → DRY → HEAT in that sequence:

Mitsubishi Electric recommends that you set your AC on the AUTO mode so that the cooling unit adjusts to change in room temperature based on the set temperature.

The Heat Mode has not yet Taken Effect

When you start the Heat mode on your Mitsubishi AC, the unit will take a few minutes before it can start to blow warm air. This is not a malfunction and should not cause you to panic.

When the Heat Mode on your Mitsubishi AC has not Taken Effect

Allow the AC to warm up and wait until the unit starts blowing hot air without switching the AC off or trying out other commands on the remote control.

The AC is too Small for the Space

Air conditioners are built in sizes that are measured in BTUs: the amount of energy they will be used to heat/cool a specific size of space.

If your AC has lesser BTUs than you need to heat your space, then its energy is not enough to heat the room.

How to Tell if your Mitsubishi AC is too Small for the Space

Follow these steps to tell if your Mitsubishi AC is too small for the space:

  1. Calculate the size of the room/space you want to heat in square feet by multiplying its length and width.
  2. Check the BTU rating of your AC from the label plate or the User’s Manual.
  3. Visit the Energy star website and find the Energy Star Room Air Conditioner Buying Guide. This guide will show you what number of BTUs corresponds to what size of space. If your Mitsubishi AC BTU rating is smaller than what is required for the space you calculated, then it is too small for heating the space.

Note that other space factors may affect how well (or not) your AC heats the space you want to be heated:

  • Your room’s ceiling height.
  • The climate of your location.
  • The quality of your home insulation (walls, windows, and doors).
  • Your home design (if your home has open floor designs it will require more energy than enclosed rooms).

How to Fix a Mitsubishi AC that’s too Small for the Space

There are two ways you can resolve the issue of an AC that’s too small for the space:

  1. Pair the AC with another one to supplement the heat deficit from your AC.
  2. Replace the small-sized AC for one with the number of BTUs required to sufficiently heat the space.

Mitsubishi Air Conditioner Not Cooling/Not Cold

If your Mitsubishi air conditioner is not cooling, the outdoor unit is dirty, the AC is wrong-sized, the air filter is clogged, the AC has low refrigerant levels, or the AC thermistor is bad. A dirty air filter is the most common cause for a Mitsubishi AC not cooling and can be fixed by cleaning.

Unmaintained Outdoor Unit

A Mitsubishi outdoor unit houses key components of the cooling system like the condenser coil, compressor, fan, and electrical parts. Because of its consistent exposure to rain, sunlight, and debris, the outdoor unit of your Mitsubishi AC needs regular maintenance.

If this is not done, accumulated debris, dust, and other particles can block the airflow and limit the amount of air that is cooled. 

Also, accumulated heat due to a dirty outdoor unit can cause your AC not to cool as it should. A Mitsubishi outdoor unit should be well maintained through regular cleaning. 

How to Diagnose a Dirty Mitsubishi AC Outdoor Unit

The first sign of a dirty outdoor AC unit is poor airflow. However, to confirm that your outdoor unit is dirty, you’ll need to open the top panel by unscrewing it and looking inside to notice any debris that’s stuck in parts of the AC. Look out also for accumulated dust on the condenser coil fins.

How to Clean a Dirty Mitsubishi AC Outdoor Unit

To clean your Mitsubishi outdoor unit, follow these steps:

  1. Stop the AC’s operation and switch off the power at the circuit breaker. 
  2. Remove the screws of the top panel and place the panel aside.
  3. Remove the screws that hold the discharge grill and place the grill aside as well.
  4. Unfasten the screws of the front panel and remove the panel. Doing so will reveal the main parts of the outdoor unit including the fan, condenser coils, compressor, and electrical parts.
  5. Use a low-pressure hose to pass water on the condenser coil fins and the fan. You can use a soft brush to remove any stubborn dirt from the fins but be sure not to bend any of the fins as this will compromise the airflow. Also, ensure no water goes to the electrical parts. Most designs have the electrical part and the compressor partitioned so this should be easy to do.
  6. Wash the front and top panels with water and leave them to dry. Allow the condenser fins and fan to dry completely too.
  7. While the wet parts are drying, use a damp cloth to wipe any dust from the electrical parts and compressor. Be extremely careful not to cause any damages.
  8. Once everything is dry, screw back the front panel, discharge grill, and the top panel in that order. Ensure the screws are tight as loose screws can cause unintended noise from loose parts.
  9. Switch the AC back on and resume operation.

If you do not feel up to the task, and especially if you are not sure you can keep the electrical part dry while you clean your Mitsubishi AC outdoor unit, get a reliable HVAC expert to do the job for you. We can send one to you immediately as soon as you fill and submit the form at the bottom of this article.

Wrong-sized AC Unit

If you’ve installed your Mitsubishi air conditioner recently and it not cooling or not cooling enough, the AC unit could be too big or too small for the space that needs cooling. 

A Mitsubishi AC that’s too big for the space being cooled is rated higher (in BTUs) than what you need for the space. As a result, your room cools faster but with uneven distribution of the cooled air. This causes the compressor to run for shorter cycles leaving your room feeling warmer. 

Instead, if your Mitsubishi AC is too small for the space being cooled, it is rated lower than what you need to cool the space. In this case, the AC compressor runs nonstop, causing the heat from the cooling process to take up the cooled air and the humidity levels to remain unaltered. Besides, a perpetually running AC could easily malfunction.

How to Diagnose a Wrong-sized Mitsubishi AC Unit

Your Mitsubishi AC has a BTU rating or the amount of energy required to provide cooled or heated air for a space in square feet.

To make out if your Mitsubishi AC is the wrong size for your room, check its BTU rating and read the corresponding space size (in square feet) from a reliable guide like the Energy Star Room Air Conditioner Buying Guide. If the BTU rating corresponds to a lower or higher space size than what is shown, then your Mitsubishi AC is wrong-sized.

How to Fix a Wrong-sized Mitsubishi AC Unit

Ensure you buy the right size of Mitsubishi AC for the space you want to cool from the very beginning. You can do that by:

  1. Calculating the size of the space in square feet (multiply width and length) and then checking the corresponding BTUs for the space on the Energy Star Room Air Conditioner Buying Guide. You can then proceed to buy a Mitsubishi AC with the right BTU rating. 
  2. Consult an expert HVAC for proper buying guidance before proceeding to purchase the AC. We can connect you with a reliable HVAC expert as soon as you fill and submit the form at the bottom of this article.

Note: If you’ve already purchased a wrong-sized Mitsubishi air conditioner, replace it with the correct size as this will save you money in energy bills and ensure you get the proper cooling for the room. 

Clogged Air Filter

Cooling relies on a steady airflow in and out of the AC unit. If your Mitsubishi AC has a dirty and clogged air filter, the airflow is compromised and your unit will not cool as it should. The obvious solution for a dirty air filter is to clean it if your AC has a permanent filter or replace it if your AC uses a disposable filter.

How to Diagnose a Dirty/Clogged Mitsubishi AC Air Filter

To check whether your Mitsubishi AC air filter is dirty, open the front panel of the indoor unit to reveal the filter and check it for dirt and clogging.

How to clean a Dirty/Clogged Mitsubishi AC Air Filter

Mitsubishi Electric recommends cleaning your AC air filter every 2 weeks to enhance AC efficiency and avoid inflated power consumption.

Follow these steps to clean your Mitsubishi AC air filter.

  1. Switch off the power supply to the AC.
  2. Lift the front panel of your indoor wall unit until you hear a click, then hold the hinges and pull the panel towards you to take it out. Wipe the panel with a damp cloth before putting it aside
  3. Unclick the air filter and pull downwards to remove it. 
  4. Use a power vacuum to clean a filter with light dirt. If the filter is heavily clogged, wash it in lukewarm water and leave it aside to dry completely. 
  5. If your model has an Air Cleaning Filter (a second filter fitted within the air filter at the lower frame), clean it in a similar way as the air filter every 3 months and replace it every year. 
  6. Use the Mitsubishi MAC-093SS Quick Cleaning Kit to clean the heat exchanger and the fan before replacing the air filter. See details of the entire process of assembling the kit and cleaning the wall unit in this video.
  7. Place back the air filter once dry and replace the front panel ensuring it clicks back in place.
  8. Switch the AC unit back on and resume operation.

Low Refrigerant (Freon) Level

If your Mitsubishi AC is low on refrigerant due to a leak, your AC will not cool as expected. This is because the refrigerant is supposed to absorb the heat from the air during the cooling process. If the AC is low on refrigerant, it will not absorb the heat or cool the air fast enough, causing it to work extra hard. Besides low refrigerant and continuous cooling can cause the coils to freeze up.

How to Diagnose Low Refrigerant Levels in Mitsubishi AC

If your Mitsubishi AC is low on refrigerant, you will notice some or all of these signs:  

  • AC not cooling, or not cooling enough.
  • Frozen evaporator coils.
  • A rattling sound from the AC’s compressor.
  • Longer cooling cycles than the typical 10-15 minutes.
  • Higher power bills from your AC’s extra work.

A professional diagnosis is required for low refrigerant levels. As such, you should call a professional HVAC if you notice the above signs and you have checked for all other causes of a Mitsubishi AC not cooling.

How to Fix Low Refrigerant Levels in a Mitsubishi AC

Fixing AC refrigerant issues requires professional HVAC skills. You should, therefore, call a Mitsubishi AC expert to ascertain that your AC is low on refrigerant, evacuate it of the existing refrigerant, and recharge your AC with the recommended level of refrigerant.

Since this is a costly service, you might want to talk to the HVAC professional about the better option between recharging the AC with refrigerant and buying and installing a new one. We can help you with finding a reliable Mitsubishi HVAC professional once you fill and submit the form at the bottom of this article.

Bad Air Conditioner Thermistor

The thermistor is a part of the AC that works with the thermostat to send signals to the compressor and fan when it’s time to start running and cool air for your room (once the temperature you’ve set on the thermostat is surpassed).

If the thermistor is bad, it will not send the required signal to get your AC running and your room will not be cooled. Alternatively, you might also see incorrect temperatures displayed on the thermostat or extreme temperature fluctuations. All this does not let your AC cool as it should.

How to Diagnose a Bad Thermistor on your Mitsubishi AC

The first sign of a bad AC thermistor is irregular cooling cycles. Your AC will cycle on and off randomly without following the typical 10-15 minute rotations. 

A bad thermistor will also display incorrect room temperatures, oftentimes showing extremely high-temperature levels at one time and extremely low-temperature levels the next minute.

Apart from these signs, you can manually check if your AC thermistor is failing by following these steps:

  1. Turn off the power to your AC unit from the circuit breaker.
  2. Remove the dust cover of your wall unit and place it aside.
  3. Open the front panel of your AC wall unit and remove the air filters.
  4. Unscrew the outer casing of the AC wall unit and remove it to reveal the inner compartment and electrical unit.
  5. Identify the thermistor wire and test it for continuity using a multimeter. If it does not show power flow, have it replaced.

How to Fix a Bad Thermistor on your Mitsubishi AC

It is best to call a professional HVAC technician to carry out the testing and replacement of a bad thermistor, especially if you are not sure you can do the above process correctly.

Frozen Evaporator Coil

The evaporator coil is a part of the indoor AC unit that absorbs the heat from the air so that it can be sent as cool air to your home.

If the evaporator coil is frozen due to poor airflow (the air filter is clogged, the airways are blocked, there’s a refrigerant leak, or the AC is short cycling), it will not absorb the heat and your AC will not blow cold air.

How to Diagnose Frozen Mitsubishi AC Evaporator Coil

To check if your Mitsubishi AC evaporator coil is frozen, open the front panel of the indoor unit and pull out the air filter to reveal the coil. Check for any signs of ice build-up.

Even before opening your cooling unit, you may tell that your AC has a frozen evaporator coil if you notice:

  • Leaking water from the indoor unit.
  • Sweat-like moisture droplets on the outer casing of the indoor unit.

How to Fix a Mitsubishi AC Frozen Evaporator Coil

Perform the following if your Mitsubishi AC evaporator coil is frozen:

  1. Allow the ice on the evaporator coil to thaw by switching off the cooling unit until all the ice disappears.
  2. Take care of the underlying cause:
  • Clean a dirty air filter.
  • Remove any barriers on your AC’s airway.
  • Call an expert HVAC to resolve refrigerant leak issues.
  • Attend to issues that are causing your AC to short-cycle such as electrical faults with the compressor, fan motor, thermostat, or capacitor.
  1. If you want to speed up the thawing process, set the AC to Fan mode at high fan speed for 15 minutes.

Mitsubishi Air Conditioner Not Turning On/Not Starting

If your Mitsubishi AC won’t start, the wall outlet could be faulty or has an overload, the circuit breaker may be tripped, or the power cable may be faulty. These are not common faults but, you can avoid a wall outlet overload by not plugging other appliances into the same wall outlet with the AC. 

Wall Outlet Overload

Electrical wall plugs are made with a standard voltage load. If too many appliances are plugged into one wall outlet through an electrical extension or adapter, the wall outlet could have an overload and short. 

How to Check and Prevent Wall Outlet Overload

A typical electric wall plug can handle 1,800 watts, which is what most breakers carry: 15 amps and supply 120 volts (Watts = A x V). You can also have a breaker size of 20 amps supplying 120 volts which is around 2,400 watts.

For example, if your Mitsubishi AC already takes up 1,600 watts of a 1,800 watts outlet, it should not be plugged into the same wall outlet with other appliances to prevent overload.

As a rule, plug only your AC into the wall outlet and do not use electrical extensions as these can have voltage differences.

Tripped Circuit Breaker

A surge in the power supply can cause the circuit breaker to trip. This means the breaker shuts electrical flow to protect the circuit from overheating and the consequent damage or electrical fire. A circuit breaker may also trip due to a ground fault or a short circuit.

Even when the power supply is normalized, your circuit breaker switch will not resolve on its own. This explains why your AC may not turn on when it needs to start a cooling cycle.

How to Determine if a Circuit Breaker is Tripped

To check if the circuit breaker supplying power to your Mitsubishi AC has tripped, open the circuit breaker panel and check if the switch is down (switched off).

How to Fix a Tripped Circuit Breaker 

If the circuit breaker is tripped, carefully turn the switch back on by lifting it up. Note that you should not try to force a circuit breaker switch back on if it feels hard to move as that could mean more damage.

If the circuit breaker is not tripped (all switches are turned on) but no power is being supplied, the circuit breaker could be faulty and you need to call an expert electrical technician. 

Damaged Mitsubishi AC Power Cord

This is not a common occurrence, but a Mitsubishi AC power cord that’s not transmitting voltage will cause your AC not to turn on. Also, AC power cords with physical signs of damage such as a broken or frayed cord are faulty and should not be used in the first place.

How to Diagnose a Faulty Mitsubishi AC Power Cord

To test if your Mitsubishi AC power cord is damaged:

  • Notice any physical signs of damage (breakage or frayed cords). 
  • Test the power cord for continuity using a multimeter in the following steps:
    1. Unplug the power cord from the wall outlet and remove the other end from the AC.
    2. Set the multimeter to continuity test mode (you will see a volume indicator).
    3. Plug the positive lead to the ohmmeter/voltmeter outlet and test for an open circuit with one of the multimeter lead by touching one of the prongs of the AC end of the power cord. If there’s continuity, the multimeter will beep. If not, repeat the test with the second prong to confirm that the AC cable is faulty. If no beep is heard both times, the power cord is open and needs to be repaired or replaced.

How to Fix a Faulty Mitsubishi AC Power Cord

Electrical AC issues should always be left to a trained HVAC or electrical expert. As such, never attempt to repair faulty power cables by yourself as this could cause damage to your AC or initiate electrical fires.

If your Mitsubishi AC power cable does not show continuity, contact a Mitsubishi dealer near your place for replacement or get help using the Mitsubishi Electric Telephone Support page. You can also seek direct help by calling the Mitsubishi Electric Trane HVAC US customer care number (1-855-923-3631).

Mitsubishi Air Conditioner Keeps Turning Off

A Mitsubishi air condition that keeps turning off has power supply issues (most common), a faulty thermostat, low refrigerant levels, or the AC could be too big for the space being heated. Also, the thermostat could be installed in a bad position where room temperature cannot be correctly detected.

Power Supply Issues

An unreliable power supply is probably the first thing you should think of if your Mitsubishi air conditioner keeps turning off. That could mean regular power surge or short circuits, a loose power cable, or defective electrical wires of the thermostat, compressor, fan motor, or control board.

How to Diagnose Power Supply Issues in a Mitsubishi AC

Check to ensure that your Mitsubishi AC power cable is not loose as this could cause it to go on and off depending on when electrical contact is complete or broken. This is most likely to happen at the side that’s connected to the AC. 

Monitor the circuit breaker to see if it has regular power surges or short circuits. 

Test cables and AC parts you suspect have power issues for continuity using a multimeter. You can check the User’s Manual of your Mitsubishi AC to find out how much voltage the cable or AC part should be recording. 

How to Fix Power Supply Issues in a Mitsubishi AC

Replace an AC power cable that is loose and does not provide consistent power. You can do that at the Mitsubishi dealer closest to you or contact Mitsubishi Electric Support. 

If your Mitsubishi AC has parts that do not record continuity, call an expert HVAC technician to attend to the issue and don’t attempt resolving it by yourself. We can send you an HVAC pro to help you with Mitsubishi AC power issues once you fill and submit the form at the bottom of the article.

A Faulty Thermostat

The thermostat controls the cooling cycles in a Mitsubishi AC by signaling the compressor and fan to start running when the set temperature is surpassed and to stop running when the set temperature is achieved.

If the thermostat is faulty so that it sends a ‘stop cooling’ signal before the typical 10 to 15-minute cycle is complete, your Mitsubishi AC will keep turning off. This means your space will never be cooled as it should.

How to Diagnose a Faulty Mitsubishi AC Thermostat

Check your AC thermostat and notice if the set temperature keeps fluctuating from abnormally high to abnormally low temperatures. 

Also, notice if your AC thermostat turns off and on due to power issues as this also means your AC is short-cycling.

How to Fix a Faulty Mitsubishi AC Thermostat

A faulty Mitsubishi AC thermostat will need to be replaced. Contact an HVAC pro and have the expert confirm that the thermostat is indeed faulty before replacing it with a functional one.

Bad Thermostat Position

An AC thermostat works by detecting the surrounding temperature levels and then signaling the AC to start or stop cooling depending on the prevailing temperature.

If you position your AC thermostat in a location where there is secondary heat or cold (where there’s a cooler or direct sunlight), it is going to be recording faulty room temperatures depending on whether it is running the Heat or Cool mode.

Consistent secondary cool air will make the thermostat continuously signal the AC to turn off.

How to Diagnose Bad Thermostat Positioning

Try to temporarily eliminate the source of secondary cool air and see if the problem with your AC turning off continuously is resolved. That could mean moving the cooler or other sources of cool air away from the thermostat.

How to Rectify Bad Thermostat Positioning 

If temporality eliminating the secondary source of cool air resolves the issue with your thermostat, relocate the thermostat to a central position where it can detect the room temperature correctly. 

The AC is too Big for the Space

If you have a Mitsubishi AC that has a higher BTU rating than what’s needed for the space you are cooling, the AC will go for shorter cooling cycles (keep turning off in shorter cycles). This is because more cool air will be dispensed quickly and the space around the cooler will be cooled fast.

But, that also means the air distribution will not happen gradually and there will be an uneven distribution of cool air: you will feel cooler in one position and warmer in another position of the same room.

How to Tell if your Mitsubishi AC is too Big for the Space

Follow these steps to tell if your Mitsubishi AC is too big for the space being cooled:

  1. Calculate the size of the space you are cooling in square feet by multiplying its length and width.
  2. Check your Mitsubishi BTU rating from the label plate or the User’s Manual.
  3. Visit the Energy Star website and check the Energy Star Room Air Conditioner Buying Guide to determine if the BTU rating on your Mitsubishi AC corresponds to the size of the room you are cooling. If the size of the room is smaller than what is recommended for your AC’s BTU rating, then your AC is too big for the space being cooled.

How to Fix a Mitsubishi AC that’s too Big for the Space

Follow the above steps to determine the size of AC you need for your space before purchasing your Mitsubishi air conditioner.

If you are already using an AC that’s bigger than what’s needed for the space being cooled, consider replacing it with the correct size as this will save you money in power bills. The cool air from your AC will also be evenly distributed.

Low Refrigerant Levels

The refrigerant in your AC has the function of absorbing the heat from the cooling process. If your Mitsubishi AC is low on refrigerant due to a leak, it will not perform its heat-absorbing role properly and the cooling process will not run smoothly. This could mean that the pressure levels in the compressor are altered and your AC will keep short-cycling.

How to Diagnose Low Refrigerant Levels in Mitsubishi AC

A low refrigerant level in an AC is a diagnosis that can only be made by a professional HVAC technician. However, if you notice any of the following signs, your AC could be low on refrigerant/Freon and you should consider calling a professional Mitsubishi AC expert:

  • The AC is not cooling or is not cooling enough.
  • The evaporator coils are frozen.
  • There’s a rattling sound from the AC’s compressor.
  • The AC goes for shorter or longer cooling cycles than the typical 10-15 minutes.
  • You are paying higher power bills lately.

How to Fix Low Refrigerant Levels in a Mitsubishi AC

Call an expert HVAC pro if you notice any of the signs of low AC refrigerant levels. The HVAC expert will: 

  1. Confirm whether or not your AC has low refrigerant levels.
  2. Advise you if recharging your AC with the right refrigerant levels will cost you more or less than buying a new AC.
  3. Evacuate the AC (remove the existing Freon) till the acceptance value is reached and then proceed to charge the AC with new refrigerant according to the specified levels. 

We can help you find a reliable HVAC to take care of refrigerant issues in your AC once you fill and submit the form at the bottom of this article. 

Mitsubishi Air Conditioner Leaking Water Inside

If your Mitsubishi AC is leaking water inside, the drain hose is cracked or wrongly installed, the humidity levels are extremely high, the indoor unit is installed in a slanting position, or the evaporator coil is frozen. The most common cause is a blocked drain line, easily resolved with cleaning.

Drain Hose Problems

The indoor drain hose can cause leaks if it is wrongly installed, has a crack, is bent and causes a reverse flow, or is blocked.

How to Fix Mitsubishi AC Drain Hose Problems

Ensure your Mitsubishi AC drain hose is correctly installed from the very beginning. This means that the drain hose should not be slanting upward or have any bends.

Also, ensure that the drain hose is always clear without any blocks and that it has no cracks. Replace or repair a cracked drain hose.

High Humidity Levels inside the Living Space

During the cooling process, both heat and moisture are removed by your AC from the cooled air that’s sent to your home. The moisture is then used to enhance your AC’s efficiency and any extra moisture is sent to the drain pan and out of the cooling unit through a drain pipe.

If there’s too much moisture inside your living space, plenty of moisture will be produced from the cooling process, which can cause the drain pan to overflow and leak. 

How to Diagnose High Humidity Levels inside the Home

Your AC thermostat will show the current humidity levels. Alternatively, you also can check from your smartphone weather widget.

You may also notice these signs if the humidity levels inside your home are high:  

  • A soggy feeling in the air.
  • The smell of dampness around the home.
  • A foggy build-up of moisture on the windows.

Healthy humidity levels are between 30% and 50%. If the humidity levels in your home are higher than that, your AC will likely produce extra moisture.

How to Fix High Humidity Levels inside the Home 

Even though your Mitsubishi AC will have to work harder in high-moisture conditions, moisture levels will go down after some time running the AC. Nonetheless, you can help your AC work less by reducing moisture levels by one or more of the following ways:

  • Install a dehumidifier especially if high moisture is common in your location.
  • Run your AC on the Dry Mode for 1-2 hours (not more than that).
  • Keep your HVAC ductwork in good condition and with no leaks.
  • Install ventilation fans in high moisture sections of the home like the shower and kitchen.
  • Remove indoor plants when moisture levels are high.

Uneven AC Installation

Your indoor Mitsubishi AC unit has a drain pan that collects moisture from the cooling process and sends it out of your home through the drain pipe. 

If your AC indoor unit is installed in a slanting position so that the water in the drain pan tends to go to one side, it could cause a leak.

How to Tell if your Mitsubishi AC is Installed in an Uneven Position

It is easy to tell if your indoor AC unit is slanting simply by looking at it. Differently, you can open the front panel and remove the filter to check if water from the cooling process is tending to one side of the drain pan.

How to Fix a Mitsubishi AC that’s Installed in an Uneven Position

It’s advisable to have someone with the know-how install your Mitsubishi AC right from the beginning. If a mistake was made and the indoor unit is installed unevenly, consult an expert to correct the mistake and prevent further wall, furniture, or, flooring damage from AC leak.

Blocked Condensate Drain

The entire moisture drainage path of your Mitsubishi AC needs to be clear to ensure no water is staying around your AC and not getting properly drained. This means that the drain pan should not be overflowing and the condensate pipe and main drain pipe should be clear and not clogged.

If any of these parts are blocked, the drain pan overflows and water could leak down your wall unit to the wall, ground, or any furniture below the unit.

How to Diagnose a Blocked Condensate Drain

A blocked condensate drain will cause standing water in the drain pan and eventually, send leaking water down the indoor unit.

Other signs of a blocked condensate drain include: 

  • Standing water in the drain pan.
  • A damp and moldy wall around the cooling unit.
  • A damp smell in the air vents and around the wall unit.
  • No water draining from the outdoor exit of the drain line.
  • Dirt from the drain line when you insert a long wire into the drainpipe, indicating clogging from accumulated dirt.

How to Fix a Blocked Condensate Drain

To unclog a blocked condensate drain line, follow these 6 steps:

  1. Switch off your Mitsubishi AC.
  2. Drain the standing water from the drain pan using an absorbent rag by soaking it and squeezing the water into a bucket. 
  3. Suck up the water standing in the condensate drain using a shop vacuum. 
  4. Use a plumber’s snake (if you have one) or a piece of long thin wire to remove any dirt that’s stuck in the condensate drain or the main drain pipe.
  5. Once all the dirt is removed, throw a bucket of warm water with vinegar and a bit of kitchen detergent to clear the drain of any dirt that’s stuck to the pipe.
  6. Switch on the AC and monitor its operation to see if the leak is resolved. 

Frozen Evaporator Coil

Frost on the evaporator coil happens as a result of poor airflow due to a dirty filter or blocked AC airway. Low refrigerant levels, leaking ductwork, faulty fan blower, or dirt on the evaporator coils can also cause the coils to freeze up.

As a result, the ice melts slowly during the cooling process sending extra water down to the drain pan. This could mean that the water drainage pipe is not keeping up with the large amount of water being produced, causing the drain pan to overflow and leak.

How to Diagnose Mitsubishi AC Frozen Evaporator Coil

If you notice that your Mitsubishi AC is leaking water inside, open the indoor unit to look for signs of a frozen evaporator coil:

  1. Lift the front panel of your AC indoor unit until you hear a click. Hold the hinges and pull the panel towards you to remove it. 
  2. Unclick the air filter and pull it downwards to remove it. The evaporator coil will be revealed.
  3. Check to see if there’s ice on the coil.

How to Fix Frozen Mitsubishi AC Evaporator Coil

If your diagnosis concludes that the evaporator coil is frozen, leave the AC turned off to allow the ice on your Mitsubishi evaporator coil to thaw

You can speed up the thawing process by setting the AC on Fan mode and the fan at high speed for about 15 minutes.

Mitsubishi Air Conditioner Leaking Water Outside

If your Mitsubishi air conditioner is leaking water outside, it is usually because it is working hard on a hot and humid day during the cooling season or the temperature of the condenser coil in the outdoor unit has dropped below the dew point temperature outside. Both are normal AC operations.

High Humidity Levels

On hot summer days with high humidity levels, your AC is forced to work harder to remove the heat and humidity from the air. Also, the high humidity levels come with higher condensate levels. This means more water is drained outside the home.  

Below Dew Point Condenser Coil Temperature Outside

When your AC is set on the Heating mode, the indoor unit blows warm air and raises indoor temperatures. But the outdoor unit is cool from low temperatures and can get extremely cold. 

If the temperature of the outdoor unit drops below the dew point temperature outside (the temperature at which the air cannot hold any more moisture), condensation/dew forms on the condenser coil of the outdoor unit. This water runs down the coil and collects at the base of the outdoor unit.

If your Mitsubishi air conditioner outdoor unit has a small draining hole at the bottom, this water will drain below the unit. If this is not the case, the water will overflow once the base is filled up. Both cases explain why your outdoor unit will be leaking water which, as earlier explained, is a normal operation in the prevailing weather conditions.

Mitsubishi Air Conditioner Fan Not Working

If your Mitsubishi AC fan is not working, it could be a wrong fan speed or fan mode setting, a malfunctioned thermostat, or a defective fan motor. Wrong fan speed or fan mode settings are more common causes for an AC fan not working, and this can be easily resolved with the correct setting.

Wrong Fan Speed/Mode Setting

To distribute cold or warm air, your AC fan should be set on Medium or High speed. Instead, if it is set on the AUTO mode or on low speed, the cool or warm air may not be felt and it will seem like your Mitsubishi AC fan is not working.

What to do if your Mitsubishi AC has the Wrong Fan/Mode Setting

If your Mitsubishi air conditioner doesn’t cool or heat effectively because the Fan mode or speed is wrongly set, simply use the Fan button on your remote control and press until you can choose the Med. or High speed. Your AC fan should start working.

Malfunctioned Thermostat

The fan in your Mitsubishi AC starts to run every time the thermostat sends a signal that the temperature in the room has risen above the set level. This prompts both the fan and the compressor to start running.

If the thermostat has malfunctioned, it will send faulty signals, which could be that the temperature in the room is lower than the set level always and the fan does not need to run, which is why the fan will not work.

How to Diagnose a Faulty Mitsubishi AC Thermostat

If your Mitsubishi AC thermostat has malfunctioned, it might show a blank screen or indicate extremely low or extremely high-temperature levels.

How to Fix a Faulty Mitsubishi AC Thermostat

A faulty thermostat needs to be replaced. Contact a professional HVAC if your Mitsubishi AC thermostat is acting up and giving erroneous temperature figures and have the thermostat replaced. We can hasten the process for you by sending the expert Mitsubishi AC pro as soon as you fill and submit the form at the bottom of this article. 

Defective Fan Motor

A defective fan will not serve its function of blowing cool/warm air to your room. If the fan motor is faulty or has voltage issues, it is not going to be spinning as it should.

How to Diagnose a Defective Mitsubishi AC Fan Motor

You’ll need to open the AC compartment that houses the fan and try spinning the fan manually. If the fan spins without much effort, it probably has voltage issues. But if it is hard to turn and spin, the motor bearings are most likely worn out and need to be replaced. 

How to Fix a Defective Mitsubishi AC Fan Motor

Have an expert HVAC technician check and service a defective AC fan motor. We can connect you with a reliable Mitsubishi AC expert as soon as you fill and submit the form at the bottom of this article.

Mitsubishi Air Conditioner Making Noise

If your Mitsubishi AC is making abnormal noise, the AC may have been installation badly or there are loose/broken AC parts making noise while the cooling unit is in operation. A dirty air filter is a common cause of a noisy Mitsubishi AC and should be prevented by cleaning the air filter regularly.

It’s important to differentiate between normal and abnormal Mitsubishi AC noises. Normal noises (not malfunctions) include: 

  • A gas escaping sound: This is heard when the refrigerant is flowing. 
  • A cracking sound: When the internal parts of the AC contract or expand with temperature changes. 
  • A buzzing sound: When the outdoor unit starts running. 
  • A ticking sound: When the fan of the outdoor unit is controlling airflow to ensure optimal AC operating.

Other loud noises should be considered malfunctions and can be caused by the following issues:

Improper AC Installation

Mitsubishi AC recommends that an air conditioner be installed by an expert with specialized knowledge. This is because improper AC installation can cause electrical faults, water leakage, noise from improperly fixed parts, or failure of the AC to initiate the cooling process.

How to Fix Improper Mitsubishi AC Installation

Ensure that your Mitsubishi AC is installed by the dealer or technician with specialized knowledge from the very beginning. The installer should consult the Mitsubishi AC Installation Manual for the model step by step.

If an installed Mitsubishi AC is making noise due to improper installation, consult your dealer and have the installation issue corrected.

Loose/Broken AC Parts

If your Mitsubishi AC has loose or broken parts, they will move and shake when the unit is in operation and cause a rattling noise. Loose or broken parts could be the front panel, the fan, or the air vanes. 

How to Inspect and Fix Loose/Broken Mitsubishi AC Parts

Delicate AC repairs are best done by an expert HVAC technician. Contact a Mitsubishi dealer near you or call Mitsubishi Electric Support about broken Mitsubishi AC parts. 

Ensure that the front panel and the vanes are installed according to the instructions on your Mitsubishi AC model’s Installation Manual.

If you need to fasten loose Mitsubishi AC parts and are not sure what to do, call in an HVAC pro to do the job. If you need a hand, we can connect you with a reliable HVAC pro once you fill and submit the form at the bottom of this article.

Dirty Air Filter

A dirty air filter is always bad news when it comes to air conditioners. If your Mitsubishi AC filter is dirty, airflow is restricted and the compressor will be working extra hard to supply the required cool air with little air supply. 

How to Diagnose a Dirty Mitsubishi AC Air Filter

Open the front panel of your indoor Mitsubishi AC unit by lifting the panel till you hear a click and then pulling the panel towards you while holding the hinges. Doing this will reveal the filter and you can check if it’s covered with dirt.

How to clean a Dirty Mitsubishi AC Air Filter

To clean a dirty Mitsubishi AC air filter, follow these instructions: 

  1. Switch off your Mitsubishi AC at the circuit breaker.
  2. Raise the front panel of your Mitsubishi AC indoor unit until you hear a click. Use the hinges on each side to pull the panel out.
  3. Remove the filter by unclicking it from its position and pull it downwards to take it out of the AC. 
  4. If the air filter has little dirt, use a power vacuum to clean it, otherwise, wash it in lukewarm water if extremely dirty and leave it aside to dry completely. You can wipe the front panel and the AC frame with a damp cloth while the filter dries.
  5. If your Mitsubishi AC model has an Air Cleaning Filter (a second filter fitted within the air filter at the lower frame), clean in the same way you clean the air filter. 

Mitsubishi Electric recommends cleaning the air filter every 2 weeks and the Air Cleaning Filter every 3 months and replacing it every year. 

Mitsubishi Air Conditioner Light Blinking

If your Mitsubishi AC lights are blinking, they could be indicating abnormal operation such as a faulty power control board, communication error between the indoor and outdoor units, an overheated compressor, or outdoor fan issues.

Typical Mitsubishi AC light blinking happens in normal operation when you press a button on the remote control to send a command to your AC. But, atypical blinking is indicative of abnormal operation and should be attended to by an HVAC pro, unless your User’s Manual gives simple troubleshooting guidelines.

Below are some of the most common Mitsubishi AC light blinking cases that are indicative of abnormal operation. 

Note that we can send you a reliable Mitsubishi AC professional to resolve any light-blinking AC issues as soon as you fill and submit the form at the bottom of this article.

Mitsubishi Air Conditioner Light Blinking 14 Times

Mitsubishi air conditioner light blinking 14 times is an indicator that “the power module is out of order.” This could be caused by issues with the power control board, causing key parts like the compressor to run abnormally.

How to Fix Mitsubishi AC Light Blinking 14 Times

Call in an expert HVAC technician to assess the issue by:

  1. Measuring the voltage of each of the lead wires connected to the compressor.
  2. Assess the compressor terminals for resistance.
  3. Replace the power control board if it has an irreversible malfunction.

Mitsubishi Air Conditioner Timer Light Blinking 2 Times

If your Mitsubishi air conditioner time light blinks 2 times, it has detected an “Outdoor heat exchanger liquid pipe sensor error.”

This could be caused by one or more of these situations:

  • Poorly joined connections.
  • A wire break of the outdoor heat exchanger liquid pipe sensor (a wire break is detected 15 seconds after it happens and at a temperature below -50℃. This will stop the AC operation).

How to Fix Mitsubishi AC Timer Light Blinking 2 Times

Do not attempt to resolve AC power issues by yourself. Instead, call an expert HVAC pro or a trained electrician to assess and resolve the issue.

Mitsubishi Air Conditioner Timer Light Blinking 6 Times

If your Mitsubishi air conditioner timer light blinks 6 times, there is an “Error of communication between indoor and outdoor units.”

This is usually caused by one of these situations:

  • A broken connection wire.
  • No power, or inconsistent power supply.
  • Defective outdoor or indoor unit circuit boards.
  • Poor contacting.

How to Fix Mitsubishi AC Timer Light Blinking 6 Times

Power-related Mitsubishi AC issues should always be resolved by an HVAC expert or trained electrician.

Mitsubishi Air Conditioner Timer Light Blinking 5 Times

If your Mitsubishi air conditioner timer light blinks 5 times, the AC “compressor has overheated.”

This can be caused by:

  • Low refrigerant levels.
  • A faulty vent-pipe sensor (when the value of the vent-pipe sensor exceeds the setting, the air conditioner will stop).
  • A closed disconnecting valve.
  • An overworked compressor due to other AC issues.

How to Fix Mitsubishi AC Timer Light Blinking 5 Times

Always call a reliable Mitsubishi AC expert or a trained electrician to resolve power-related issues with your AC. 

If your Mitsubishi AC compressor is overworked due to issues like poor airflow, resolve the root cause of the problem.

Mitsubishi Air Conditioner Timer Light Blinking 7 Times

Mitsubishi air conditioner timer light blinking 7 times is an “outdoor fan motor error.” This happens only with a DC motor.

The fan motor error can occur as a result of one of these causes:

  • Poor AC plug contacting.
  • A defective outdoor fan motor.
  • A faulty outdoor circuit board.

How to Fix Mitsubishi AC Timer Light Blinking 7 Times

Call a reliable Mitsubishi AC expert or a trained electrician to assess a defective motor and other electrical faults with your AC. Do not attempt to resolve them by yourself to prevent electrical accidents or damage to the AC.

Mitsubishi Air Conditioner Yellow Light Flashing

The yellow light on your Mitsubishi air conditioner is on during timing operation. If it starts flashing, it means that there’s failure in a wire connection.

Note that the yellow light on your Mitsubishi AC may start flashing when other error codes are displayed.

Mitsubishi Air Conditioner Green Light Blinking

The green light on your Mitsubishi air conditioner lights during operation. But, if the green light is blinking, the airflow has stopped due to the “CLEAN” operation.

Note that the green light on your Mitsubishi AC may start flashing when other error codes are displayed.

Note also that the meaning of blinking lights on your Mitsubishi AC may vary with different models.

Mitsubishi Air Conditioner Error Codes/Fault Codes

Mitsubishi air conditioner error codes indicate abnormal operation in your cooling system including abnormal pipe temperature, abnormal high pressure, receiving or transmitting communication error, freezing or overheating, drain overflow, or abnormality of power module among others. 

We present some of these common Mitsubishi air conditioner error codes, what they indicate, their causes, and what the HVAC pro will do to resolve them when troubleshooting is not an option.

Mitsubishi Air Conditioner Error Code P8

Mitsubishi air conditioner Error Code P8 is an abnormal “pipe temperature” error that occurs in both the cooling and heating modes of the AC.

In the cooling mode, the pipe temperature is detected as abnormal when the temperature does not get into the cooling range (-3℃) 3 minutes after the compressor starts running and 6 minutes after the liquid/condenser pipe is not in the cooling range (9 minutes in total to be detected). This error does not happen in the Dry mode.

In the heating mode, the pipe temperature is detected as abnormal when the condenser pipe temperature is not in the heating range (3℃) 20 minutes after the compressor starts running excluding the defrosting period (27 minutes in total to detect pipe temperature). 

Abnormal pipe temperature can be caused by:

  • A minor temperature difference between the indoor room temperature and the liquid/condenser pipe temperature. This may happen if: 
  • Refrigerant levels are low.
  • There’s a disconnected liquid/condenser pipe holder thermistor. 
  • There’s a faulty refrigerant circuit.
  • Bad connection of the extension pipe.
  • Wrong wiring of the indoor and outdoor units connecting wire.
  • A faulty detection of indoor room temperature and liquid/condenser pipe temperature thermistor.
  • A partially closed stop valve.

How to Fix Mitsubishi AC Error Code P8

Contact an HVAC pro to:

  1. Check the liquid/condenser pipe temperature against the room temperature displayed on the remote controller and outdoor controller circuit board. 
  2. Assess the extension pipe for a bad connection and the indoor and outdoor unit connecting wire for converse wiring.
  3. Make a temperature check of the outdoor controller circuit board.

Mitsubishi Air Conditioner Error Code 1302

Mitsubishi air conditioner Error Code 1302 (U1) is an “abnormal high pressure error.” 

This error code occurs in a variety of situations including:

  • Short-cycling of the indoor/outdoor unit.
  • Decreased airflow due to a clogged air filter or dirt on the indoor unit fan.
  • A dirty heat exchanger.
  • A malfunctioned indoor/outdoor fan motor.
  • Malfunction of fan driving circuit.
  • Defective operation or closed stop valve.
  • Blocked or broken pipe.
  • Defective thermistor that detects lower temperatures than the actual temperature.
  • Contact failure or disconnection of the outdoor controller board.
  • Malfunction of the linear expansion valve.

How to Fix Mitsubishi AC Error Code 1302 (U1)

Call an expert HVAC to resolve Mitsubishi AC Error Code 1302 (U1). The HVAC expert will:

  1. Open a semi-closed or fully closed stop valve.
  2. Assess the piping and repair any defects.
  3. Check if the thermistor-detected temperature on the LED display coincides with the actual temperature.
  4. Assess the linear expansion valve.
  5. Replace a faulty outdoor controller board. 
  6. Make a thorough check of both the indoor and outdoor units and repair any defects.

Mitsubishi Air Conditioner Error Code E6

Error Code E6 (6840) on your Mitsubishi air conditioner is an “indoor/outdoor unit communication error” or “signal receiving error” detected by the indoor unit. 

This communication receiving error will display when the indoor controller board does not receive the usual signal after power is turned on for 6 minutes or the indoor controller board does not receive any signal for 3 minutes during operation. 

Error E6 on your Mitsubishi AC can be caused by:

  • A short circuit, contact failure, or converse wiring (bad wiring) of the indoor and outdoor units connecting wire.
  • A faulty transmitting/receiving circuit of the indoor or outdoor controller circuit board.
  • Intruding noise into the indoor/outdoor unit connecting wire. (Note: Noise in an electrical circuit is the effect caused by random electrical signals that are coupled into circuits where they are not needed).
  • A defective fan motor.
  • A faulty rush current resistor of the outdoor circuit board.

How to Fix Mitsubishi AC Error Code E6 (6840)

You can try resetting the AC by turning off the power and back on again.

If this does not resolve the issue, call an expert HVAC to resolve Mitsubishi AC Error Code E6 by:

  1. Checking if the indoor and outdoor connecting wire is correctly connected or is loose. 
  2. Checking if noise entered into the indoor and outdoor connecting wire or power supply.
  3. Checking if noise entered into the indoor and outdoor controller boards.
  4. Check if the rush current resistor on the outdoor power circuit board is open and replace the circuit board if a fault is detected.

Mitsubishi Air Conditioner Error Code U6

Error Code U6 (4250) on your Mitsubishi air conditioner is an “abnormality of power module” error.

The error code will present in the following situations:

  • A closed outdoor stop valve.
  • Decreased voltage supply.
  • A loose, disconnected, or conversed compressor wiring connection.
  • A defective compressor.
  • A defective outdoor power circuit board.

How to Fix Mitsubishi AC Error Code U6 (4250)

Call a Mitsubishi AC expert to resolve Error Code U6 by:

  1. Opening a closed stop valve.
  2. Checking the stability of the power supply.
  3. Correcting a faulty compressor wiring. 
  4. Assessing the compressor for other defects.
  5. Replacing a faulty outdoor power circuit board.

Mitsubishi Air Conditioner Error Code P6

Mitsubishi air conditioner Error Code P6 is a “freezing/overheating” warning. It is accompanied by 3 times blinking on the red LED and may occur during both the cooling and heating season as per the status of the AC.

How to Fix Mitsubishi AC Error Code P6

An HVAC expert will assess and fix Mitsubishi AC Error Code P6 by:

  1. Checking whether the indoor unit is short-cycling.
  2. Checking if the filter and heat exchanger are dirty.
  3. Assessing the resistance value on the indoor and outdoor fan motors.
  4. Checking if the refrigerant pipe has signs of clogging.

Mitsubishi Air Conditioner Error Code E9

Mitsubishi AC Error Code E9 (6841) is an “indoor/outdoor unit communication error” or “transmitting error.” The error is displayed when the unit controller board does not find any transmission path for 3 minutes.

The communication transmission error can be caused by:

  • Contact failure of the indoor and outdoor units connecting wire.
  • A defective communication of outdoor controller circuit board.
  • Noise in the power supply or the indoor and outdoor units connecting wire.

How to Fix Mitsubishi AC Error Code E9 (6841)

Try resetting the AC by turning off the power and back on again to see if the issue is resolved. If not, call a Mitsubishi AC expert to resolve Error Code E9 by checking:

  1. If the connecting wire of the indoor and outdoor units is loose or disconnected. 
  2. If the outdoor controller circuit board has any abnormality or is faulty and needs to be replaced.

Mitsubishi Air Conditioner Error Code P5

Mitsubishi air conditioner Error Code P5 is an “indoor drain overflow” error. It is accompanied by 2 times blinking on the red LED. 

How to Fix Mitsubishi AC Error Code P5

Call an HVAC expert to assess and fix Error Code P5 by:

  1. Checking if the drain pump works. 
  2. Testing the terminals of the drain pump for resistance value.
  3. Assessing the drain function (blockages, leaks, or other issues).

Note that Mitsubishi error codes may vary by model but, these are the common code errors that will display when there’s an abnormal operation in your AC. If you are not sure about the displaying error on your Mitsubishi AC, you can:

  1. Fill and submit the form at the bottom of this article and we’ll send you a reliable Mitsubishi AC expert to perform the necessary service.
  2. Contact the nearest Mitsubishi dealer or get help using the Mitsubishi Electric Telephone Support page. You can also make direct calls using the Mitsubishi Electric Trane HVAC US customer care number (1-855-923-3631).

Vincent Steele

Vincent is a freelance writer based in Santa Ana, California. When he isn't writing articles for Temperature Master, he can be found biking or hanging out with his cat, Shelly.

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