What to do When AC Compressor Clutch Is Not Engaging

What to do When AC Compressor Clutch Is Not Engaging

If you experience your car’s air conditioning (AC) clutch compressor is not engaging, you may want to know why and find some answers. Here, you can learn what to do during a situation like this.

If the clutch compressor doesn’t engage, there are more possibilities. But, sure you can’t use your car’s air conditioning system when this happens. The clutch compressor is an integral part of the AC system of your car, rendering this inoperable is a big inconvenience for the car’s passengers.

Car Part

Car Part

Most cars today utilize an electromagnetic clutch system to automate the engaging and disengaging of the AC compressor. This makes operating your car’s air conditioning more convenient and user-friendly. This article will help you decide on what to do when the AC compressor clutch is not engaging.

But first, know some facts about an AC clutch compressor.

What is an AC clutch compressor

An AC clutch compressor is a type of compressor that derives its power from the car engine’s flywheel. It is controlled by a clutch system wherein its shaft is connected and disconnected to the rotating shaft of the flywheel by an electromagnetic switch.

AC clutch compressor

The clutch and compressor are two of the most important parts and the hardest working elements of your car’s air conditioning system. These parts, along with other of your vehicles’ components should be properly maintained to assure its serviceability.

How does a clutch compressor work?

To utilize the AC on your car on demand, the clutch compressor is activated. To run this compressor, the car’s engine is directly connected to the pump rotor of the compressor with a belt. Automotive air conditioning system uses an electromagnetic clutch mechanism that engages the compressor to turn the AC unit.

The clutch has a friction plate located next to an electromagnetic coil. When this is activated, a current passes through the coil creating a very powerful electromagnetic force (EMF). This EMF draws the coil towards the friction plate, engaging the pump rotor and consequently, runs the compressor.

Determining if the clutch is working

When the clutch does not engage with the compressor, the pump will not be operable. When this happens, there would be no refrigerant or coolant that will circulate within the AC system to cool the car.

To determine if the clutch is operational or not, try these techniques:

  • Switch on the AC controls to MAX AC
  • Run the engine
  • Take a closer look at the front of the clutch
  • At this time, the pulley and the clutch should be rotating
  • If the pulley is the only one spinning, the clutch is inoperative.

Possible reasons why clutch is not engaging

Here are some of the possible reasons why the clutch does not engage the compressor:

  • Could be a burnt fuse
  • Lockout on clutch sensor due to:
  1. Too low on refrigerant
  2. Overcharged with refrigerant
  3. Insufficient oil in the compressor

Possible Solutions

  • Checking the fuse

To verify whether the fuse is not busted, turn off the engine of the car and disconnect it from the system. Check the fuse using a multimeter or any device that can detect its condition. If the fuse is not blown, install it back to where you got it.

  • Defaulting on lockout

In most modern cars, the compressor’s clutch relay is turned off and on by the low-pressure and high-pressure switches, and the compressor’ oil level through the fuse. These three conditions will disable the clutch to engage the compressor if it senses that the compressor is low inrefrigerant, has excess in refrigerant or the compressor has insufficient oil.

Here are the possible steps that you can do to correct the problem.

1. Refrigerant too low

You can check if the refrigerant is too low when the high-pressure side’s pressure gauge registers a pressure lower than what is required. You can check your car’s AC manual for the correct pressure level.

There are repair kits available online such as the R410A Refrigerant Repair Kit for charging refrigerant or the Du Pont Refrigerant 134A. These come complete, including instructions.

2. Overcharged with refrigerant

If the compressor is overcharged with refrigerant, the high-pressure side will register an abnormally high pressure reading. You can check the AC’s manual for the right operating pressure on this side.

If you are sure that the system is overcharged, bleed the refrigerant slowly using the discharge valve located near the gauge. Do so until you reach the appropriate pressure level.

3. Checking oil level of compressor

The oil level of the compressor can easily be seen from its sight glass. Sufficient level is indicated by a red line in the sight glass. If the level appears way too low the red line, you must add oil. Add the type of oil compatible with the compressor.

Use only compressor oil that is approved by your AC’s manufacturer. You could check the oil’s specifications on the owner’s manual. Such oil is also available on Amazon, like the Cool Bear A/C Compressor Oil or the ACDelco 15-118 Compressor Oil.


It may not be difficult to diagnose a clutch compressor’s “malfunctioning”. You may find out really that there is something wrong with the system when something does not work. You now know what to do when AC compressor clutch is not engaging.

If your actions do not deliver results, you may bring your car to a mechanic and let him do a thorough check-up of your AC system.

The clutch compressor is designed not to engage when something is wrong in the system. So, next time, better check these things occasionally to avoid problems:

  1. Fuse
  2. Refrigerant (or coolant)
  3. Compressor oil

Find more other questions to understand more your car here

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Carolina - Care My Cars

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