How To Tell If Car AC Compressor is Bad

how to tell if ac compressor is bad

Air conditioning systems are an important part of cars and other vehicles, optimizing the environment inside the vehicle cabin. Typically, there are many different parts used in a vehicle’s air conditioner, such as the AC compressor, refrigerator, pipes, AC condenser, AC evaporator coil, expansion valve, and AC pressure switch.

But sometimes some fault occurs in the air conditioner system of the vehicle, due to which the car’s AC stops working or starts cooling less. If any part of the air conditioning system fails or malfunctions, it may stop completely. In this article, you will learn in detail about how to tell if the car’s AC compressor is bad.

What is A Car AC Compressor?

.The AC compressor is a vital component in the air conditioning system that pressurizes and circulates the refrigerant, enabling the transfer of heat from the inside to the outside environment, thereby facilitating cooling.

There is a clutch and pulley in front of the AC compressor, and when the driver turns on the AC, the clutch engages with the rotating pulley through a magnet coil, and the AC compressor starts. There are 6 to 8 small pistons installed in the AC compressor of the car, which are installed in different cylinders of the AC compressor. However, many AC compressors may also have a rotor.

But their working principle is the same. When the AC compressor is rotated by the engine, these pistons move up and down in the cylinder. The piston of the AC compressor compresses the refrigerant with high pressure and sends it to the AC evaporator coil. Due to this, the compressed refrigerant expands in the expansion valve and cools the AC evaporator, and the blower fan blows air from the middle of the cold evaporator into the AC vent, thereby cooling the environment of the vehicle cabin.

How To Tell If Car AC Compressor is Bad

If your car’s AC compressor is bad, you may notice symptoms like no cold air coming from the vents, grinding or squeaking noises, refrigerant leaking around the compressor area, excessive vibration while the AC is running, or engine overheating. On the basis of these symptoms, you can tell whether the AC compressor in the car is bad or not.

1. No Cool Air Coming From The Vents


If you turn on the AC in your car or other vehicle and the air coming out of the vents is not cool, it could be a sign of a failing AC compressor in your car. However, there could be other reasons for not getting cool air from the AC vents, for which you will need to check your car’s air conditioner system. By which you will be able to find out what exactly the problem is.

2. Abnormal Noise

A faulty AC compressor in your car or other vehicle may produce unusual noises when running. You may hear grinding, screeching, or rattling noises from the compartment near the compressor. These unusual noises from the AC compressor can often be the result of a worn compressor bearing, worn out internal parts of the AC compressor, or even a serpentine belt.

3. AC Clutch Not Engaged

ac clutch not engaging

Vehicles have a clutch to activate or deactivate the AC compressor. This compressor’s clutch is engaged with the help of a magnet coil, with the compressor pulley rotating continuously with the engine when the AC is started. If the clutch does not engage when your car’s AC is on, it could indicate a problem with the compressor magneto coil or clutch.

4. AC System Not Cut Off

The AC system has to be switched on and off from time to time to maintain the desired temperature inside the car cabin. This process is automatic in an AC compressor. But if your car’s ac compressor does not automatically cut off or continues to run when it cools down beyond the set temperature, it could be a sign of a faulty car AC compressor.

5. Engine Overheating When AC On

Sometimes, a bad or failing compressor can put extra strain on the engine. Due to which, in many cases, the serpentine belt may break and at the same time, the temperature of the engine starts rising when the AC is turned on. This is often due to jammed AC compressor bearings or wear and tear on the internal parts of the compressor. So engine temperatures rising when the AC is on can also be a sign of a bad AC compressor.

6. Leaking Refrigerant

Sometimes the rubber ring or pipe of the car’s AC compressor leaks. Because of this, refrigerant leaks from the compressor, and the air conditioner system stops cooling. There is a lot of refrigerant pressure inside the ac compressor, and when the compressor leaks, you can also hear a hissing sound coming from the leaking ac compressor. The hissing sound of refrigerant leaking from the compressor can also be a sign of a failing compressor.

How Does A Car AC Compressor Work?

The AC compressor of cars or other vehicles is driven by a belt attached to the engine. When the AC is turned on by the driver, the AC compressor is turned on via the magnet coil. When the AC compressor is turned on, the piston or rotor inside the AC compressor housing creates a low pressure area. This low pressure area allows refrigerant gas from the AC evaporator to enter the compressor.

After this, the piston or rotor of the AC compressor compresses the refrigerant gas. And the pressure of the refrigerant gas increases. The compressed refrigerant gas is discharged by the compressor in the AC condenser. The AC condessor is fitted in front of the vehicle and a fan is also fitted. High pressure gas flows through the middle of the condessor and the outside air from the condessor fan reduces the heat of the refrigerant.

The high pressure liquid passes through the refrigerant expansion valve, the expansion valve usually located at the evaporator inlet. The expansion valve controls the flow of high pressure liquid refrigerant into the evaporator. This lowers the pressure of the refrigerant, causing it to expand faster. The rapid expansion of the refrigerant inside the evaporator causes a drop in temperature, causing the evaporator to cool further.

The evaporator coil is located inside the cabin of the car and consists of a network of fans that allow air to pass over it. The cold, low-pressure refrigerant absorbs heat from the air passing over the evaporator fins, resulting in cool air. The blower fan inside the AC system blows this cool air into the cabin of the car, providing the desired cooling effect. The refrigerant, which has now absorbed heat, returns to the compressor and the cycle continues as long as the AC compressor is on.

How To Test AC Compressor In Car?

  • To test the car’s AC compressor, first start the engine.
  • Next, turn on the air conditioning system and observe or listen for the AC compressor pulley and clutch engaging.
  • If the clutch does not engage with the compressor pulley, this is a sign of a problem with the compressor.
  • But if the compressor is spinning with the clutch engaging the pulley, check the AC airflow and temperature.
  • For this, place your hand in front of the vent to check the air flow. It should be much cooler than when the AC is off.
  • Next, measure the refrigerant pressure. To check the refrigerant level and system pressure, connect an AC gauge to the low and high pressure service ports on the AC system and measure the appropriate reading.
  • Finally, you’ll need to inspect for refrigerant or fluid leaks and scan for any error codes. For this, you can use the OBD scanner tool.

Fan Kicks on But Compressor Not Working

If your fan kicks but the compressor is not working, the cause of this problem could be a faulty capacitor, which is responsible for starting the compressor. Additionally, a bad thermostat, damaged wiring, or refrigerant leakage can also cause this type of problem.


Q. Why did my AC compressor go bad?

The AC compressor can wear out over time. Due to friction, the internal components of the compressor wear out, due to which the compressor is not able to compress the refrigerant. Apart from this, the compressor can also get damaged due to damaged wiring and contaminated refrigerant.

Q. Is there a way to test an AC compressor?

If your vehicle’s AC compressor is not working, there are a few things you can do. But if you don’t have inspection experience, you should seek the help of a qualified professional air conditioning technician.

Share If You Like

Leave a Comment

error: Content is protected !!