What Should I Do If AC Compressor Clutch Is Not Engaging?


If it's a warm day and you need the AC, but when you turn it on the cool air doesn't work, then you may have a compressor clutch problem. If the AC compressor clutch stops working or doesn’t engage, your AC won't work correctly. So if you find your AC compressor clutch not engaging, it likely the problem with your AC. 

If your AC compressor clutch stops working, you need to check the electrical connections, the circuitry, the refrigerant, or you might need to service or replace your AC compressor.

Even if your using the correct refrigerant and oil for your AC system, the clutch can still have electric faults. A problem in the circuitry could cause the clutch not to engage. We rely on our air condition so much that we need it to work properly when it's supposed to. We'll discuss steps to take in various situations.

Checking the Clutch and Further Steps

AC compressor is not engaging

Photo Credit: https://www.youtube.com/watch?v=9yEGurt9th4

Take a Look First

If you've turned on your car and turned up the AC to high, and no cold air comes out, it's time to check the AC compressor clutch. Turn off the car and look at the clutch. It should turn freely if you rotate it.

Look at the compressor and clutch. They should be free of rust, having a clean healthy looking belt on pulley, and the wires should all look like they're making good connections.   

Next, you can turn on the car and put the AC to high. Open the hood and look at the compressor clutch. Give it a minute and see if it is engaging and disengaging at regular intervals. If it does, this is a sign that the clutch is probably doing fine.

Power Testing

If the AC compressor clutch has not engaged after a minute or two, you may want to jump-start the clutch to check if it is still working. Turn off the car, but turn the key so the power is on.

You can check to see if the clutch wires are getting power with a multi-meter. Another option is to connect extra wires from the battery to the clutch wires and see if the clutch engages.

You can also opt to buy a car diagnostic tool like in the video to test for power and clutch operation. (Amazon Link)

If the clutch isn't getting power, then this may be due to a faulty relay or pressure switch. If you connected power manually from the battery, and the clutch does not engage, you'll likely to need a new clutch.

If it's an old compressor and clutch, or you've had problems with the AC system in the past, both the clutch and compressor should probably be replace.  

It might be important to replace the clutch or clutch and compressor immediately, so other problems don't occur with your AC system. 

Check the Relay

In some of the cars, the compressor clutch relay goes on and off due to the low-pressure switch. (Amazon Link)  The relay is however grounded by a computer in a controlled system. Try to inspect all the components of the system to diagnose the issue faster. 

Get a digital voltmeter (Amazon Link) and check the voltage and the ground of the compressor. If you are unable to get the voltage reading, check the fuse. (Amazon Link)

If all is fine with the fuse, you need to check the clutch relay. (Amazon Link) Pull it and check for both power and ground on the relay through its terminal sockets. 

Clutch Problems

Turn all the controls of your AC to MAX and start the engine. Observe the clutch and the compressor. The clutch at times, and compressor pulley, should be spinning. If only the pulley spins, there is a problem in the system.

A non-engaging clutch could be due to the following reasons. A blown fuse, a bad coil, low-pressure lockout (a possible leak in refrigerant), poor ground, bearings lock up, slipping clutch, a short in the wiring, or a belt may be misaligned.

In some vehicles, the power flows from the AC switch to the fuse and then gets directed from the fuse to the clutch, as the low-pressure evaporator temperature changes. You could check the wiring for problems if that seems to apply to you, but this usually isn't an issue.

Just make sure if there was any work done on your AC compressor previously, that oil was added if needed to prevent a mechanical failure.

Compressor Issues

To see if the compressor might be the problem, you can turn off the car and take off the belt to the compressor. Make sure you use the correct tool on the tensioner pulley to take the belt off, and then try turning the compressor pulley manually.

If it's under pressure, then it might take some effort to turn, but should turn. 

If it wont turn, something might be broken or not working correctly inside, and should be replaced.

Reconditioning a compressor can be costly, since there are so many way for things to go wrong. Your best bet is to get a new compressor and clutch if possible to avoid future problems.  

Being Low on Refrigerant

AC compressor is not engaging

Photo Credit: https://mike-thomson.com/blog/?p=1240

Being low on the coolant is one reason why you will find the AC compressor clutch not engaging. Low coolant content or pressure is dangerous for the system of your car. Even though DIY kits can be used to recharged, this is also one of the major and common reasons why the compressor clutch sometimes fails to engage.

Try not to use DIY kits that work by hotwiring the low pressure switch, so the clutch will engage. This might work at times, but is considered dangerous because the compressor may lack oil.

This might actually cause some serious damage to your compressor. Lack of oil in the compressor can permanently ruin it, and send metal bits to other parts of the AC system, calling for a more extensive repairs and replacements.

If there is a leak in the system, you need to get it repaired first. Use refrigerant, but do not forcibly charge the system. A leak causes moisture and air to make its way to the system. Moisture can combine with your coolant and generate acid or sludge. This can potentially wreck the system. If this has already happened, you would need to evacuate the system out at a mechanic.

Repair any leaks in the system and then you can add refrigerant. Adding more refrigerant can be done by most people. However, you will need the tools and special gear to safety add refrigerant to your car. 

After filling or refilling your AC system with refrigerant, you can try starting the engine of your vehicle and check the compressor clutch again.

If ​the AC compressor clutch is still not engaging, you should take your car to the nearest service center or garage or give the local mechanic a call.

Replacing your Compressor

If you've come to find out you need to replace your clutch, most of the time it is cost effective to replace the compressor as well.

If they are both getting old, or the compressor is in a very difficult area to work on, then you most likely want to replace the compressor too, if the clutch is bad.

You can  replace the compressor by yourself if you have some car repair experience and have the tools needed. Make sure your ready to invest the time and energy, along with making a few mistakes along the way, when replacing your compressor and clutch. 

Our Advice

As you investigate the problem with your AC compressor clutch, start with the easiest steps, like checking for a bad fuse or checking for power to the compressor, before starting any repair work. Your car’s health is important, but your time and money is important too.

Whether it's the refrigerant or the wiring to the compressor, you need to be careful to investigate thoroughly before taking any action. 

Try not to experiment beyond your capacity. If you are unable to get the clutch to engage on your own, ask for help or call a mechanic. Check out our website for more information on auto engines, auto parts, and associated automobile problems.

Additional Questions

What if the clutch works but compressor doesn't?

After checking for proper electrical connections, fuses, and AC pressure; consider lack of oil in system, condenser issues, or some type of system blockage.

 What if my compressor is making noise?

This could be due to several problems, including the belt, pulley, bearings, the seal, or other parts that are misaligned, worn, or old.