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How To Diagnose A Bad Or Failing AC Compressor

- Jan 16, 2019 -

How to Diagnose a Bad or Failing AC Compressor?

The AC compressor is one of the most important, if not the most important, components of a vehicle’s air conditioning system. It is responsible for pressurizing the AC system and keeping the refrigerant flowing so it can function properly. Because it functions in a continuous cycle on and off, it is subject to wear every time the AC is turned on. Just like any other component on a vehicle, it will eventually fail and need to be replaced.

AC Compressor

The compressor is responsible for pressurizing and distributing the refrigerant, so if there is any problem with the compressor, the rest of the air conditioning system will be affected. Usually, when a compressor begins to fail, it will produce any of these 4 warning signs that alert the driver of the problem.

1. Cabin Temperatures Higher than Normal

One of the first signs that a compressor may be having trouble is the AC no longer blowing as cold as it once did. A damaged or failing compressor will not be able to properly regulate the refrigerant flow in the AC system, and as a result, the AC will not function properly. It may even still work, but the temperature of the air it blows out will fluctuate.


2. Loud Noises When the Compressor is Running

Loud noises when the AC is switched on is another potential symptom of a failing AC compressor. Much like other accessories driven by the engine’s belts, the AC compressor has several interior components and uses a sealed bearing to turn. If any of the interior components break, or the compressor’s internal bearings fail or seize, then all sorts of noises can be produced as a result. A leaking or worn out bearing will produce a high pitched squealing or grinding sound, while a seizing or seized bearing will produce a grinding noise or a noticeable belt squeal. Due to the complexity and nature of how compressors are assembled, it is usually easiest to replace the entire compressor instead of attempting a repair.


3. Visual Inspection Shows Damage to the Compressor or Belts

Premature wear or damage to the compressor and compressor belts will also cause the AC compressor to fail. Rust, physical damage, oil leaks, or paint damage can cause the ac compressor to stop functioning correctly. The lack of oil will cause the system to wear out faster and increase friction between the parts, leading to erratic temperatures when the AC is turned on in the car. Cracked or splitting belts will also contribute to compressor damage and will need replacement along with the compressor.


4. Compressor Clutch is Not Moving

Another sign of a problematic compressor is the clutch not moving. The clutch on the compressor is what allows the pulley to engage and disengage from engine power, so the compressor is only turning when it needs to. The clutch can seize — which permanently keeps the compressor activated — or it can break, which means the compressor will not be able to receive engine power. Sometimes the clutch itself can be replaced, but usually replacing the entire compressor turns out to be the most efficient repair.


The AC compressor is the heart of the AC system. If you suspect your AC compressor or another component of your vehicle’s AC system is having issues, consider having the system diagnosed by a professional technician. If necessary, they will also be able to replace the AC compressor for you.

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