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Air Conditioner Compressor | How It Works & Troubleshooting

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Air Conditioner Compressor | How It Works & Troubleshooting


A compressor is the engine of an air conditioning system. It’s the part that changes the refrigerant from a cool, low-pressure liquid to a hot, high-pressure gas, and then back again. This temperature change is used by the other components of the air conditioning system to create cool air, which has vastly improved the lives of anyone living in a hot country such as Australia.

In this article, we’ll explore how an air conditioner’s compressor works, some basic advice on how to maintain it, and some help with troubleshooting potential problems.

How an air conditioner’s compressor works

Refrigerant is the magical substance that makes air conditioning possible. It’s a fluid that can repeatedly change from low-pressure liquid to high-pressure gas. When in its low-pressure state, refrigerant is cool and causes evaporation when it meets warm air, which cools the air down and lowers the temperature. When refrigerant is in its high-pressure state, it’s hot and condenses when it meets cool air. This heats the air up and increases the temperature.

This change from high-pressure to low-pressure is possible because of the compressor, which is the part of the AC system that sits outside. It’s main job is to raise the temperature and pressure of the refrigerant vapour, so that it causes evaporation when it cools down, and produces cool air for your home.

The air conditioner’s compressor works by compressing refrigerant vapour, which increases its pressure and turns it into a hot gas. The cooling/condensing of the hot gas is achieved by drawing ambient air through the condensing coil using a fan, which leaves as hot air. As the refrigerant gas cools, it turns into a liquid, and the compressor pumps it indoors towards the evaporator. At this point, it passes through a restrictor or expansion device, which lowers the pressure of the refrigerant and causes evaporation, which cools the air down. It’s then pumped back outside to the compressor again to restart the cycle.

There are three common types of air conditioning compressors—the reciprocating compressor, the rotary compressor, and the scroll compressor. Most modern air conditioners use a scroll type compressor. A scroll-type compressor is tough to explain with words alone—this video does an excellent job of explaining how it works, using animated illustrations.

The compressor is connected to the rest of the system with copper refrigerant piping, which allows the refrigerant to circulate. It also requires a power source, and so much be connected to the electricity in your home.

How to maintain an air conditioner compressor

Provided your AC system is regularly serviced (we recommend once a year), your compressor should take care of itself. They typically last for about 10 to 15 years.

The one thing that you can do to prolong your compressor’s life is to keep your outdoor unit (also known as the condenser unit) free from any leaves and other debris. When these build up, they can damage the compressor, the fan, or the condenser, so it’s important to keep it as clear as possible.

Air conditioner troubleshooting compressor problems

Before we start, we want to make it absolutely clear that you should not attempt to mechanically fix your compressor yourself. It’s a complicated piece of machinery that requires specialist training to understand, and the odourless, tasteless, and invisible refrigerant gas used in an AC system can kill you if you inhale too much.

What we can recommend are some non-mechanical solutions, and pointing out the causes of common problems so that you better understand the issue.

AC compressor issues

Air conditioner compressor won’t turn off

If the AC compressor is failing to turn off, check the evaporator coil for ice. Ice build-up can mean that the system is losing refrigerant, or the evaporator coil may be blocked with dirt or debris. This is a serious issue that needs to be fixed right.
The ice build-up can also destroy the compressor over time.

The AC failing to turn off may also be due to a broken thermostat, which is failing to measure the temperature and so keeps the system running.

Finally, dirt on the condenser coil can trap heat into the AC system, forcing it to work harder to reach the set temperature.

Air conditioner compressor running but not cooling

If the indoor unit is producing hot air, and you haven’t accidentally activated “heat mode,” it’s likely that the system’s refrigeration cycle isn’t working properly or may have a refrigerant leak.

Fan blocked or damaged

If the fan in the outdoor unit is blocked or damaged, it will struggle to expel warm air from the system, leading to failure. Turn the AC unit off and check that the back of the outdoor unit is free from obstructions and debris.

Ticking sounds

If your compressor is making a ticking or clattering sound, it’s likely to be an issue with the electrical controls/inverter assembly or the compressor has mechanical issues .

Air conditioner compressor very loud

If your air conditioner compressor is extremely loud, it can (understandably) upset your neighbours, especially if the system is running overnight.

Non-mechanical AC compressor fixes

How to reset air conditioner compressor

To reset the air conditioner compressor, you’ll essentially need to reset the whole system. You can do this by following this process:

  1. Turn off the AC system using your remote or wall controller.
  2. Locate the AC’s Outdoor Power isolator switch and turn it off for five minutes. Then turn them back on.
  3. Turn on the AC system using your remote.

If this does not work please contact our Service Department where we can have an expert Service Technician diagnose the problem.

How much is an air conditioner compressor?

Unfortunately, air conditioner compressors are expensive. You can expect to pay anywhere from $1,500 to $4,000 for a replacement, which includes labour costs. Repair options also tend to be limited for compressors, so depending on the type and age of your system you have, your air conditioning technician may suggest replacing the entire system, as this can be more cost-effective. Air conditioning systems also tend to get more efficient with time, so installing a modern system is likely to reduce your power bill.

An air conditioner couldn’t work without a compressor—it’s the engine that drives the system’s fundamental process: changing the pressure levels of the refrigerant to create cycles of cold and heat. This wonderful technology has made people’s lives infinitely more comfortable the world over, and we can be thankful that we have it.