Everything You Need to Know About Your Air Conditioner Compressor

Amy Pawlukiewicz
Written by Amy Pawlukiewicz
Updated January 11, 2022
Woman smiling in kitchen
Photo: F.J. Jimenez / Getty Images


  • Four main AC parts: expansion valve, compressor, condenser, and evaporator.

  • The compressor moves warm air into the refrigerant.

  • Compressor problems are the most common AC issue.

  • Repairing a compressor costs $50 to $150 per hour, plus parts.

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You’re sitting in your home on a hot summer day, enjoying the cool air blowing from your air conditioner, when suddenly you hear an unsettling noise and the whole unit shuts down. Hmm, what to do? Understanding the air conditioner compressor—the main component used to start the cooling cycle—will help you troubleshoot and figure out what you can fix yourself, and when you need to call in a pro.

What Are the Parts of an Air Conditioner?

First, a little AC 101. There are four main parts that compose an air conditioner: the expansion valve, the air conditioner compressor, the condenser, and the evaporator. All four parts work together to suck air in, cool it off with refrigerant gas, and blow it into your house. If your air conditioner malfunctions, understanding these parts can help you troubleshoot to solve the problem.

What Does the Compressor Do?

If there are any HVAC terms you need to know, compressor is definitely one of them. The compressor handles the middle steps of the air conditioning process, taking the warm outside air and moving it into the refrigerant. 

Via a chemical reaction, the refrigerant converts the warm air to cool air, which then gets blown into your home. As the air cools, the refrigerant becomes heated air, which the compressor takes and blows out of your home. This is why you might notice your window AC unit blowing hot air as you walk by. Who knew?

How to Know if Your Compressor Is Malfunctioning

When the compressor on your air conditioner is malfunctioning, you’ll likely notice one (or more) of these issues: noises, it’s not cooling air, or it’s struggling to start. Keep in mind that your compressor may make noises as it starts up, but the noises shouldn’t persist for more than a few seconds. If you experience any of these three problems, it’s best to call a local air conditioning professional to take a look at your unit.


If you hear clanging or banging noises coming from your air conditioner, your compressor probably has a loose part, while hissing or bubbling noises are indicators of a leak in the compressor.

Not Cooling Off

One of the main ways you know when your AC unit isn’t working is that it’s not doing its main job—cooling. When the compressor in an air conditioning unit gets worn out, or if it comes loose, it can’t do its job properly and won’t cool your home.

Struggling to Start

When you turn on your air conditioner, if it struggles to start up—sometimes called a “hard start”—there may be something wrong with the electrical part of the compressor. 

Repairing the Compressor

Air conditioner repair
Photo: A Stockphoto / Adobe Stock

Most pros will charge anywhere from $50 to $150 per hour for repairs, plus whatever the cost of materials is. There are a few steps your pro will likely go through to attempt a compressor repair. 

  • Changing the belt

  • Tightening the compressor mount

  • Tightening the compressor bolts

  • Charging the refrigerant

Cost of a New Compressor

Unfortunately, when a problem arises with the compressor, it often has to be replaced. New compressors usually run between $800 and $2,800 for parts and labor, with an average national cost of $1,200. If the entire HVAC system needs to be replaced, that usually has a cost range of around $5,000 to $10,000, so it’s worth having your compressor checked before making the decision to get a new unit.

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