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Furnace Making Pulsing Noise? 3 Common Causes (+ Fixes)

Furnaces are pretty noisy appliances in general. While some subtle sounds are considered normal, when these noises turn into loud pulsing noises, it usually signals something is wrong. A furnace making a pulsing noise often signifies loose or failing parts that interfere with the furnace’s functionality. 

Your furnace is making a pulsing noise because there are loose parts in the furnace, the panels on the compressor are loose, or the fan motor is faulty. To fix the problem, check for loose parts, fasten loose screws on panels, and inspect the fan motor and fix or replace it.

This article explains why your furnace is making a pulsing sound. I’ll also help you determine the most effective way to fix the issue, restore harmony in your home and prevent future complications. 

Loose Parts Inside the Furnace

The furnace consists of multiple parts — each part plays a role in ensuring the HVAC system functions normally. A majority of the hardware found inside the HVAC system has moving parts. And when these parts are loose, they tend to make a pulsing noise when you turn on the furnace. 

Many people think that a loose part in the furnace will create a rattling sound, but this isn’t always the case. When there’s a pulsing sound, walk outside and find the compressor. Maybe that’s the source of your issue.

How To Fix

You’ll find multiple parts installed in the compressor. You should switch off the entire HVAC system before attempting to open up the compressor. Here’s what to do next:

  1. Get a screwdriver to open up the panels on the compressor. 
  2. Remove the front panel and look inside. You might notice the part that’s not connected correctly immediately. But most of the time, you’ll need to wiggle a few parts a bit to identify the loose pieces. 
  3. Check the coil fan and the fan motor. The fan blades may be loose. 

If you’re able to find a loose part, fasten it. The specific method for fastening the part depends on which piece is loose. You may simply need to fasten a screw. In other cases, you need to get a wrench to tighten loose bolts. Or you might even need to use glue to fix something into place.

Even if you don’t find any part that wiggles, you should still get a screwdriver and wrench. Gently fasten all screws and bolts in the compressor. Sometimes, hardware can be loose but not enough to wiggle when trying to move it. 

The Panels on the Compressor Are Loose

Speaking of loose parts, I should also address that panels may cause a pulsing sound. If multiple screws have fallen out of a panel, the loose part will make a loud pulsing sound whenever the furnace is on.

However, a panel that’s only slightly loose will slightly vibrate. That can also create pulsing sounds. 

A loose panel isn’t a severe problem but can still lead to complications. For example, when the top side of the panel is loose, water may enter the compressor when it rains. This can lead to electrical problems with the entire HVAC system and create an electrical hazard in your backyard.

Additionally, if the panel is loose enough that you can remove it without tools, you need to consider your children’s safety. Kids love to explore, and removing the compressor panel will expose them to dangerous moving parts and circuitry.  

How To Fix

Determining if there are loose panels on the outdoor compressor isn’t really difficult. It just takes a few seconds to check the panels. Thankfully, fixing this problem is just as easy.

First, locate the compressor. This is the large component mounted outside. The compressor has a metal sheet housing. You’ll find that the panels are fastened to each other with bolts or screws. 

While the furnace is on, see if the panels are vibrating. The movement is caused by air flowing through the compressor. If you notice a panel isn’t tightly fastened, you’ve probably found the source of the pulsing noise.

Grab an appropriate tool and fasten the panel. Fasten screws and bolts tightly. Ideally, use some thread-locking fluid. This ensures the noise is eliminated and prevents it from recurring in the future. 

The Fan Motor Is Faulty

Sometimes, fixing the pulsing noise isn’t as simple as fastening a bolt. There are times when a more serious problem is to blame for the annoying sound, such as a faulty fan motor. 

Consider that the fan motor runs continuously when you power on the HVAC system. It pulls air from outside and pushes it inward toward the furnace.

It’s common for the fan motor to give you some trouble as it gets older.

How To Fix

Don’t immediately blame the fan motor when you hear a pulsing sound coming from the furnace. You should first test the motor to see if you can find any problems. Here’s how.

  1. Power off the HVAC system.
  2. Open up the compressor to gain access to the fan motor.
  3. Disconnect the fan motor from the control board. 
  4. Once removed, see if you can manually spin the blades on the fan. Use your hand to rotate them. They should rotate about two revolutions without any resistance. 
  5. If there’s resistance, you need to fix or replace the motor.

If there was no resistance when you tried to manually turn the blades, plug the motor back into the control board. 

Turn the power to the HVAC system back on. Switch on your furnace and take a closer look at the fan. See if the fan is moving at an adequate speed. A faulty fan either won’t move or will be very slow. 

If the fan motor is faulty, contact an HVAC expert to replace it.

Summary

A faint pulsing noise from the furnace is often normal but still worth checking. Sometimes, a screw or bolt needs to be tightened. Other times, the fan motor needs replacing. 

Even when the problem isn’t serious, never ignore sounds coming from the furnace. Get an HVAC expert to inspect your furnace to avoid future complications that could end up costing much more.