Ultimate Guide to Air Conditioner Compressors

Have a question about your Air Conditioner Compressor? You’ve come to the right place. This guide to air conditioner compressors is designed to answer the common questions about a/c compressors, from what they are to why they might freeze up. Along the way, we’ll link you to some other articles where you can get more information about specific topics covered in this guide.

What is an a/c compressor and how does it work?

The compressor is a very important part of your air conditioner. It is the pump that moves the refrigerant through your air conditioning system. In most home units, the compressor is located in the outdoor unit next to your house. It takes refrigerant from inside your home, compresses it (makes it smaller) and sends it through the condenser, which is the part of the outdoor unit that cools the refrigerant and sends it inside to the evaporator coil.

Learn more about how your air conditioning works

How to tell if your ac compressor is bad?

Most people find out their compressor is bad when the air conditioning stops cooling and a technician finds the problem. You might notice some symptoms before it gets to that point.

  1. Your electricity bill is rising, but it hasn’t been especially hot and your a/c hasn’t been running more than normal. While this doesn’t always mean your compressor is at fault, it shows the efficiency of the system has been reduced and a poorly performing compressor is a big reason you’d see significant efficiency problems.
  2. Knocking, hissing or a long-startup when the system turns on. These are all signs that the compressor could be bad.

There are a lot of other air conditioning components, some of which can cause similar symptoms when they fail, so it is always best to have a repair technician properly diagnose the problem before concluding that the compressor is the issue.

What Causes the Compressor to Fail?

There are a number of problems that can cause an HVAC compressor to fail. The two most common are floodback and slugging.


Refrigerant in your system is supposed to return to the compressor as a gas. Compressors pump gases, rather than liquids. If there is a problem with the system, the refrigerant may return from the evaporator as a liquid instead of a gas. This is when floodback occurs. While floodback may be the most common cause, it is also a symptom of a problem elsewhere in the system that needs to be corrected.


Slugging is similar to floodback, since it also involves liquid entering the compressor. The damage can be quite similar, although the cause of the problem is usually different. When slugging occurs, the liquid (usually refrigerant, but it could be lubricant) enters before the compressor is running, rather than while it is running.

Other causes of compressor failure may include:

  • system leaks
  • dirty evaporator coil
  • dirty air filters
  • dirty condensers
  • component failure

How to Prevent Air Conditioner Compressor Failure

If you revisit the list above, you’ll notice that “dirty” is a repeat offender in things that can cause compressor failure. In addition to that, dirty filters and evaporator coils may also be causes of floodback. So, the best thing you can do for your air conditioning system is to keep it clean. That starts with air filters. They need to be changed regularly to keep your whole system clean.

Learn how to select the best air filter

Beyond changing your air filter regularly, routine maintenance will help identify system leaks, dirty components and other problems. This will allow you to fix your system prior to breakdown and better protect your compressor.

Need Routine Maintenance in the Charlotte Area?

Contact Us

How much does a home AC compressor replacement cost?

Compressors are generally the most expensive replacement part in a system, but there isn’t one specific cost. The range is something like $450-$3,000. The total cost depends on a number of things.

  • Is your system under warranty?
  • What is your tonnage?
  • What level of performance is your system?
  • What brand?
  • Cost of labor in your area

System Warranty Coverage

Warranty coverages vary by brand and model. Most major brands now provide 10 year parts warranty on the compressor, this includes Trane, the brand we install. Some lower-cost brands may only warranty parts for 5 years. In almost all cases, there won’t be a labor warranty after 2 years. When we make a repair, we provide a 1-year warranty on that repair. Every installer and repair company will have their own warranty and rules when it comes to labor.

If your system is outside the 10 year warranty on parts, it may be more cost effective to replace your outdoor unit and evaporator with a new one rather than fix a decade old system.

Learn More About Air Conditioner Replacement in the Charlotte Area 

System Size

A two-ton compressor costs less than a 5-ton compressor. So there will be a sliding scale in terms of parts costs (if not under warranty) and larger AC units may also increase the labor and related costs (like pumping down the coolant, refilling the coolant afterwards, etc).

System Type

Condenser units come in single stage, 2-stage, and variable stage systems. These and other differences in the existing unit may impact the cost involved, with more expensive original units also costing more to repair.


Different brands are built differently and have different costs associated with their parts. This won’t impact the labor side of things as much, but cost could fluctuate on the parts by quite a bit. You have to use a matching brand compressor because while air conditioners operate in much the same way, the specifics of sizing and technology vary by manufacturer.

Your Location

We all know that the cost of living in Charlotte is different than even the cost of living in New York City. Depending on where you live, your costs for labor are going to be different because of different wage levels and taxes/licensing fees. Level of competition in a particular place may also impact the cost of service.

To get an accurate quote on replacement, taking into account all of these factors, you’ll need to contact a qualified HVAC company.

What Causes An Air Conditioner Compressor to Freeze Up?

The two main reasons your AC unit may be freezing up are that

  1. Your refrigerant is expanding more than it is supposed to (and thus getting colder than it is supposed to).
  2. There is an airflow problem so hot air is not warming the coil back up and keeping it at proper temperature.

Want to Learn More ?- We’ve Published an entire article on Why Your A/C Ices Up.

Need Air Conditioner Compressor Troubleshooting and Repair/Replacement in Rock Hill, SC?

Contact Us