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How To Stop a Portable AC Unit From Leaking (14 Effective Tips)

A portable AC unit can leak due to several reasons, so you need to detect the problem to fix it, and consider a few preventive measures to stop it from leaking. The following solutions cover every typical problem that can cause your portable AC unit to leak.

Here’s how to stop a portable AC unit from leaking:

  1. Level the appliance perfectly.
  2. Seal the drain cap properly.
  3. Reshape the vent hose assembly.
  4. Clean the drain spout and hose.
  5. Ensure the drain line is sloped.
  6. Clean the condensate tank.
  7. Inspect the condensate pump.
  8. Seal the gaps around the ports.
  9. Clean or replace the air filters.
  10. Check for a faulty float switch.
  11. Seal any cracks in the system.
  12. Replace any broken components. 
  13. Clean the entire portable AC unit.
  14. Prevent the coils from freezing.

A few preventive methods are related to specific types of installations, such as a gravity-fed drain line or condensate pump. So you’ll need to select the solutions that apply to your installation. Read on as I explain a proactive approach to stop a portable AC unit from leaking. 

1. Level the Appliance Perfectly

All portable AC units have a float switch. This water level detector prevents leaks due to an overflowing condensate tank or drain pan. If the water reservoir, basin, or pan of your portable AC unit is not level, the float switch will not work as it is designed to function. 

That means that the condensate tank or drain pan may overflow without triggering the internal float switch and stopping the portable AC. In effect, the excess water may leak through the tiny gaps around the unit’s base. 

To avoid drainage problems and leaks, level the appliance perfectly.

Residential floors are not perfectly level, while carpets can facilitate a slight slant causing the portable AC unit to tilt on a side or the front. A backward slant should not incapacitate the float switch to the extent of causing a leak due to overflowing. 

But it is always ideal to level the unit.

2. Seal the Drain Cap Properly

Portable AC units are either partially or fully evaporative appliances. The latter is relatively new, so most people will usually have a partially evaporative unit. 

A partially evaporative portable AC unit disposes some moisture through the exhaust duct or vent hose. However, the condensate tank or drain pan will have water accumulate in due course, which could be a lot on humid days when the evaporation rate is slow. 

The accumulated water in the condensate tank or pan can leak if the drain cap is not completely sealed. Your portable AC unit may have one or more spouts, plugs, and drain caps, so seal all of them snugly.

3. Reshape the Vent Hose Assembly

Many portable AC units have very little water buildup because they dispose of the condensate as moisture through the vent hose, as facilitated by evaporation. Hence, some manufacturers do not have a large water tank or pan in their models, which has an inherent problem.

Extremely high relative humidity and seasonal precipitation can impair the normal functioning of your portable AC unit. The appliance won’t be able to dispose of as much moisture as it must to prevent water overflow in the unit. With the drain cap sealed, the excess condensate can leak.

Also, if it is raining outside, water can seep in through the vent hose or exhaust duct. This issue worsens the condensate problem with limited evaporation in the unit. So you’ll want to consider reshaping the vent hose assembly near your window. 

An inverted U or S-shaped alignment of the vent hose can prevent rainwater from seeping into the duct. Also, this can prevent excess moisture from backing up inside the hose that can trickle down as water droplets to the portable AC unit. 

This video from LG demonstrates how you can reshape the vent hose assembly (~0:45):

4. Clean the Drain Spout and Hose

If you have a gravity-fed drain line or a condensate pump, check the spout and hose to ensure they are clear. A clogged drain hose and spout will prevent efficient drainage, leading to excess water buildup inside the condensate tank. 

In normal conditions, an overfilled condensate tank or drain pan should trigger the float switch. 

The portable AC unit should shut down and display an error code. However, you may have a leak before the float switch does its job. Or, the switch can fail, and you will have a mess. 

Here’s how to fix this:

  1. Clean the drain spout to remove any gunk or grime. 
  2. Flush the drain hose with pressurized water or compressed air.
  3. You may use bleach or vinegar to eliminate mold and algae from the hose. 

These steps apply to both gravity-fed drain lines and hoses connected to a condensate pump. 

5. Ensure the Drain Line Is Sloped

A gravity-fed line or hose should be sloped downward from the portable AC unit to the floor drain or outside. Any upward gradient along the line can cause water to back up inside the hose. Thus, your portable AC unit may leak. 

Also, you should ensure the drain line is not pinched or jammed anywhere. The condensate must flow smoothly from the drain spout, through the hose, and wherever the line ends.

6. Clean the Condensate Tank

Portable AC units may have a removable condensate tank that you should empty when necessary. Some models may not have a reservoir or basin that you can take out. Instead, such units have a drain pan that can only be drained through the spout fixed to the unit. 

Irrespective of these variables, you should clean the condensate tank or drain pan. These fixtures may have debris buildup in due course, including grime, rust, or other issues. Such gunk will reduce the total capacity of the tank or pan. 

So, you may have water overflowing sooner than later. 

Also, a corroded and cracked tank may leak water through the drain pan. This problem doesn’t trigger the float switch because water will leak even before the tank is full. Cleaning the tank and pan will help you detect such an issue before you have severe water damage in your home. 

7. Inspect the Condensate Pump

Only a few portable AC units have an internal condensate pump. Most models require you to use an external condensate pump if a gravity-fed drain line is unfeasible. Thus, you must check if the external condensate pump is working properly. 

Otherwise, you may suddenly find a pool of water under and around your portable AC unit. 

Similarly, an internal condensate pump should function optimally to prevent an excessive water buildup inside the unit. So, check if the hose connected to the unit’s condensate pump through the spout is draining the water consistently.

Like a gravity-fed drain line, a hose connected to an internal condensate pump requires routine cleaning. Thus, flush the hose to ensure it is clear of clogs, mold, algae, or other gunk. Then, you can tell if the internal condensate pump is faulty and subsequently repair or replace it.  

8. Seal the Gaps Around the Ports

Portable AC units have several ports, and ideally, a flawless installation should seal these ports and prevent them from becoming vulnerable to leaks. However, in reality, some of these ports often have air gaps.

The exhaust duct or vent hose has the largest port on a portable AC unit and the biggest hole in the window bracket. Manufacturers use different materials to seal these ports. 

For instance, this Black+Decker Portable Air Conditioner (available on uses foam cotton on the window sill and around the unit’s vent outlet. Dual-hose portable AC units have two large vents. Thus, you may have four major air gaps in the system, two each on the unit and the window. 

All these air gaps or poorly sealed ports can leak. Also, the air gaps reduce the efficiency of your portable AC unit. Fortunately, you can use things like duct tape to seal these ports effectively. 

Similarly, check and improve the seal around the drain cap and other ports. 

Unlike HVAC systems and mini-split air conditioners, portable AC units are usually temporary installations. Also, their portability enables users to move them around to different rooms if and when needed. 

These maneuvers can compromise the seals and increase the chances of leaks.  

9. Clean or Replace the Air Filters

Dirty air filters are a typical reason for portable AC units leaking. So, you should clean the air filters as frequently as you can, subject to their condition and your usage. 

Most portable AC units have at least two air filters. Clean them and replace either or both when they are no longer usable. Otherwise, dirty air filters will impair the unit’s efficiency and cause unusual condensation inside the portable AC. 

Thus, the appliance may leak even when it should not.

Clogged filters prevent sufficient air flow into, out of, and inside a portable AC, and the hot and cool air will create a hotchpotch within the unit. A natural byproduct is excess condensation which will give you an overfilled tank or pan. Your energy consumption will also spike unnecessarily.  

10. Check for a Faulty Float Switch

If your portable AC unit is perfectly leveled and the drain cap is sealed properly, a leak might then be due to an overflowing tank or pan due to a faulty float switch. 

Also, you may have a gravity-fed drain line or a condensate pump, either internal or external. Even if the hoses are clogged, or the water is not draining for any reason, the float switch should stop the portable AC unit before the condensate tank or pan begins to overflow. 

Therefore, you should not have any significant water leaks. If you do, the float switch is faulty. Or you might have one of the other problems I discuss below.

A faulty float switch may or may not be replaceable, subject to the portable AC model. Besides, the float switches on many units are not easy to replace for most users. Because the water level detector is a safety feature, a certified technician or the manufacturer might be able to help you with this issue. You might not want to fix it yourself.

11. Seal Any Cracks in the System

By now, you must have already stopped a portable AC unit from leaking. Otherwise, you may have a more serious problem, i.e., structural issues. Portable AC units are not the sturdiest household appliance, certainly not anywhere as durable as large centralized HVAC systems. 

So, your unit may have cracks or other structural damages somewhere. These cracks or any opening can cause water to leak out, irrespective of the condition of the condensate tank or drain pan. The reservoir or basin doesn’t need to overflow for cracks to leak water. 

If you can find evident cracks on the unit or in the system, you must seal them using a suitable solution. You can use caulk or similar sealants on structural cracks of the portable AC unit. 

Any cracks or holes in the hoses may require foil tape, or you should replace them. 

12. Replace Any Broken Components 

A portable AC may leak if a major component is broken inside the unit. 

Consider the fans, for example. A portable AC has a blower and an exhaust fan. Either unit failing means your unit will have improper airflow, inadequate cooling, poor exhaust, and unusual condensation. Thus, you may have too much condensate in the tank or drain pan. 

Also, the condensate drips from and around the components in your portable AC. For instance, the cooling coils containing the refrigerant, the evaporator, and the condenser have a steady flow of water trickling down to the tank or drain pan. 

If the unit has structural damage, water may leak through these broken parts. So the solution is to replace the broken parts and repair the structural damage of the unit, if possible. 

13. Clean the Entire Portable AC Unit

All AC units need a routine cleaning, be it portable, mini-split, or centralized. Every significant part of your portable AC unit will have dust, dirt, and grime buildup in time. Also, you must clean the rust from the metal components, such as the evaporator, coils, condenser, and other parts.  

14. Prevent the Coils From Freezing

Last but not least, you should prevent the coils from freezing if you want to stop a portable AC unit from leaking. 

A frozen cooling coil can have significant ice buildup throughout the evaporator unit, which will melt and increase the water flow to the condensate tank or drain pan. Also, the water doesn’t necessarily drip in an orderly fashion, and the unit may have internal spills and overflows. 

Cleaning a portable AC unit and the other proactive methods in this guide should prevent the coils from freezing. If the coil does freeze suddenly, ask a technician to check the coolant level in the unit. A low coolant level is a typical cause of frozen AC coils.

Key Takeaways

Here’s a chronological summary of how to stop a portable AC unit from leaking:

  • Level the appliance and ensure all the outlet ports are properly sealed. 
  • Review the vent assembly, clean the drain line, and align the hoses correctly.
  • Clean the air filters or replace them and check for broken parts. 
  • Replace faulty components, such as the float switch, condensate pump, etc. 
  • Seal or caulk any cracks and other structural damages in the unit.
  • Clean the entire portable AC unit and prevent the coils from freezing. 


  • Steve Rajeckas

    Steve Rajeckas is an HVAC hobbyist with an avid interest in learning innovative ways to keep rooms, buildings, and everything else at the optimal temperature. When he's not working on new posts for Temperature Master, he can be found reading books or exploring the outdoors.

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