AC Compressor Clutch (Signs, Testing & Replacement)

ac compressor

No one wants to drive around in smoldering heat without ice cold air. When the ac in your vehicle doesn’t deliver, it can make the driving experience really miserable. Don’t be without your ac on a hot summer day. Read this article to find out how to troubleshoot the ac compressor clutch for the ac in your vehicle to get that ac back to cooling you off.

How Does Your AC System Work?

Your car’s air conditioning system is comprised of several parts which work together to keep you cool in the summer heat. The ac compressor clutch (view on Amazon) is a very integral part of the air conditioning system in your car. The compressor clutch regulates the ac compressor On or OFF status. There is a clutch that drives the ac compressor (view on Amazon).

Important: If you want to save $100s in servicing, diagnosis, and repair costs, improve your car's performance significantly and increase its value by 1.2x with little effort, download our Beginners Auto Maintenence & Repair Manual now. 

The compressor pushes refrigerant to an evaporator where it is condensed. The refrigerant then goes through lines and is cooled by the radiator. Cold air is pushed through your air conditioner vents and cools inside your car. All of the components must work in order for the air condition to work.

Causes of an AC Compressor Clutch Gone Bad

A bad clutch can put a damper on your ac system and leave you with hot air. Many times, the clutch is the first thing to go. There are a few common causes for a bad ac compressor. It somewhat depends on the make and model of the vehicle, how many miles are on it, and such. Here are the common causes of a bad ac compressor clutch.

Defective CAN bus – The Controller Area Network (CAN bus) is the communication link between the parts in your car. The CAN bus allows the engine communication units (ECUs) to communicate with each other by transforming sensor data over CAN frames. When the CAN bus is damaged, it can affect the ac system as well as many others.

Broken ground wire – The ground enables functioning in electrical wires. When the ground is bad, the electrical currents are forced to find other paths to the battery. You may see your lights flicker or dim uncontrollably.

Corroded or open wires in CAN bus harness – Corrosion is an enemy to electrical wires and connectors. When the wires are corroded or open, sensor problems follow. This can be the basis for your ac system problems, including the ac compressor clutch.

No Maintainance – If you fail to maintain your vehicle, it can lead to the ac compressor going bad and this isn’t something you want to experience. Failing to maintain your vehicle can lead to certain components going bad and this can cause knock-on effects with other components. If you want to prevent this from happening, you’ll need to make sure that you look after your vehicle.

If you want to avoid ac problems or other issues and save $100s of dollars that you’ll spend at the auto repair shop, you’ll need to service your vehicle often – you can use our mechanic-rated Auto Maintenance and Repair Manual to do this. It’s basically what mechanics use to go through your vehicle to check if there are any problems that need fixing. As soon as they notice the most minor problem, they’ll ask you to fork out some money even though it’s a problem you can fix yourself in minutes – the manual will teach you how to maintain your vehicle every few thousand miles and it’ll teach you how to fix minor problems that mechanics will ask you to pay for; saving you money in the long run.

A lot of our readers have the Auto Maintenance and Repair Manual printed on their garage wall and 92% of them haven’t visited the auto repair shop in the last year because they know what to do to avoid problems. All it takes is giving your vehicle a little attention every few thousand miles and you’ll never spend money at the workshop again.

Symptoms of an AC Compressor Clutch Gone Bad

The ac in your car is not functioning properly, there is a good chance that the problem is associated with the ac compressor clutch. There are a few signs that the ac compressor clutch is failing or has gone bad. Here are a few signs that the ac compressor clutch has a problem:

AC is blowing hot air – This is an easy way to tell that your air conditioning system needs attention. If you turn on your ac and hot air comes out of the vents, there’s something wrong.

Check Engine Light (CEL) – The Check Engine Light (CEL) on your dash will activate to let you know something is wrong. You can use an your OBD2 Scanner (view on Amazon) to see if the trouble codes have anything to do with the ac system.

Leaking refrigerant – The ac compressor is designed to prevent the refrigerant from leaking while it is being pressurized. When the ac compressor becomes worn, the bearings are damaged. The refrigerant is allowed to leak through the bearings. You may see the leak near the compressor. This is sign that your ac compressor bearings have worn out.

Noises from the compressor – You may hear what sounds like squealing noises when the belt is worn out or damaged. Turn the engine ON. Then turn the ac ON and listen. If you hear weird noises coming from the ac system, there is a good chance that your compressor clutch is bad.

How to Test Your Ac Compressor Clutch

So, you’re ready to test because you know that the ac in your car cannot function properly without the ac compressor clutch. There are a few things that cause your clutch to go bad, so if you’ve seen signs, you’ll need to troubleshoot first by testing the system. Here are the steps to test your ac compressor clutch:

Check for a blown fuse

Put the vehicle in park – Make sure the car is turned OFF, in park, and with the emergency brake ON. Then raise the hood.

Test your battery strength – You will need a voltmeter. Take the positive end of the voltmeter and touch the positive terminal on the battery. Turn the gauge on the voltmeter to “volts”. Check to see if the number on the gauge is less than 12.5 volts. If it is, the ac compressor will not turn on. You need to charge the battery. If the reading is still low, you may need to replace a cell or use another battery.

Start the engine – It is time to warm up the engine. Start the car and stand in front of the Ac compressor under your hood. If you are not sure where the ac compressor is, look in the owner’s manual or the factory manual for your vehicle. You should see the ac clutch engage and begin to spin. If it does not spin, turn the car OFF. Disconnect the negative terminal cable from the post.

Replace the fuse – Find the fuse box. Now find the fuse for your ac. If you are not sure which one is for the ac, look at the diagram for your fuse box. If the fuse is blown when you pull it, replace. Now find the ac relay fuse. Plug in another fuse of the same amperage. Reconnect the negative terminal cable to the post. Turn the car ON and turn the ac options on HI. Check to see if the clutch will engage. If it does, it was a bad fuse.

Check the refrigerant levels

Connect the compressor – Your vehicle should use R13 or R134a refrigerant. If it uses R12, hook the ac gauge hose to low side nipple of the compressor. Connect the high hose to the high side compressor nipple. If your car uses R134a refrigerant, connect the low hose to the 13 mm compressor nipple. Then connect the high hose to the 16 mm compressor.

Check the PSI

Check the PSI – Start the car and turn the ac options to HI. Open the low and high side buttons on the gauge. Check the reading. The PSI for the low side should be 25 to 40. The PSI for the high side should be between 200 and 225. If your reads are not within these parameters, or you do not see any charge, the problem is the cutout relay in the compressor. The relay is blocking any voltage from activating the clutch. The ac must be charged up with refrigerant.

Check the clutch pulley belt

Tighten the pulley belt – The AC belt can become damaged or even break. The pulley belt connects the ac compressor clutch to the engine crankshaft so that the compressor will come on when the car is turned on. Turn the engine OFF. Have a look at the pulley belt to see if there are any contamination or cracks. Also, check for the correct tension. There should not be any more than a quarter inch of play in the belt. If there is play, loosen the mount bolts at the base of the compressor. Now loose the top adjusting bolt. Pull the compressor against the pulley belt until there is no slack. Go back and tighten all the bolts. You can also tell that the belt needs replacing if you cannot defrost your windshield.

Listen to your clutch with a Mechanic’s stethoscope probe

Use a mechanic’s stethoscope probe (view on Amazon) to listen to your clutch. Turn the engine ON. Put the probe on the clutch in an area that is not moving. Turn the ac options on HI. Listen for any noises coming from the clutch. Check to see whether the clutch is engaging and spinning. If you hear noise from the clutch and maybe the compressor, but the clutch is not engaging and spinning, there is most likely a short in the internal clutch. If there is a lot of movement in the clutch pulley, the shaft bearings could be worn out.

Check the shaft bearing seal

Check for contamination on the seal – Turn the engine OFF. Take the three bolts holding the faceplate and remove the plate from the clutch. Check the shaft bearing seal for any type of residue such as oil film. If you see residue, the seal is functioning properly and refrigerant is being discharged from the ac system. Replace the shaft bearing seal and recharge the system.

Clean the wire connector

Clean the connector – Turn the engine OFF. Disconnect the wire connector and clean the contacts. You can use a paper towel or cotton with electrical spray. After cleaning the contacts, turn the engine ON and turn the ac options to HI. Place a jumper wire on the positive battery terminal while at the same time touch the wire to the wire connector hot wire on the clutch side. Check to see if the clutch engages and spins. If it does not, the problem is an internal short.

Check the OBD2 Trobe Codes

Use an OBD2 Scanner – The OBD2 Scanner will show you the trouble codes for your vehicle. There are codes specifically for the ac system components. For example, you may get the P0645 “A/C Clutch Relay Control Circuit” trouble code which means your ac is probably not working due to circuit. This code may not activate the CEL for a while.

What to Do if the AC Compressor Clutch is Bad

You know you have a problem, you’ve tested, now it’s time to fix it. Most likely, you will have to replace some parts. Repairing or replacing an ac compressor clutch, relay or other related parts can be expensive so check to see if those parts on your car are still under warranty first. It may be that you can get help with the repair cost.

Safety First

You can drive without the ac compressor clutch because the ac pulley is free spinning with the clutch. If the clutch does not work, it won’t directly affect the rest of your car. Although you can drive with a bad ac compressor clutch, you shouldn’t. Once you have isolated the problem to your ac system, go have it checked by a professional. See if they come to the same conclusion. These types of repairs require experience with electricity, compressors, and using special tools. If you’re not sure what to do, let someone else help you. Stay cool.

Job Guthiri is a freelance writer with 3 years of experience writing for Motorsrun and other established automobile outlets. His focus and key interests are Tacomas and maintenance. Read our Editorial Guidlines and Fact Checking process.