AC Compressor Clutch Always Engaged: 6 Reasons Why?

When you see that your AC compressor clutch always engaged, it means the refrigerant inside your car keeps on freezing. It will be solved if you replace or fix the compressor switch.

This guide will help you understand the continuous engagement of the AC compressor clutch and why it is a problem when it always stays engaged. 

Table of Contents

AC Compressor Always Working: 6 Reasons

There are multiple reasons why this might happen, but when it does, there are some simple repairs you can carry out yourself that are usually effective. Here is a table of the possible causes of a faulty AC and what you can do about them:

Low-Pressure Switch MalfunctionReplace the malfunctioning low-pressure switch.
Refrigerant Overcharge or UnderchargeCheck refrigerant levels 
Refill the refrigerant
Compressor LeakageUse a UV light to detect refrigerant leaks
Repair or replace leaking components
Faulty Relays or WiringCheck the relay. 
Inspect wiring for shorts or damages.
Faulty Parts Replace the faulty parts with new ones.
Short Circuits or Electrical FaultsInspect the wiring for damage or incorrect connections.
Ensure the relay isn’t stuck closed; 
Replace it if necessary

Now, here are the reasons why AC compressors are always working and the solutions in detail. 

Low-Pressure Switches:

Pressure switches in the AC system, such as the low-pressure switch, high-pressure switch, or evaporator temperature sensor, play a role in determining when the compressor should engage or disengage. A malfunction in these switches could cause the compressor to stay engaged at all times.

Solution: Replace the malfunctioning low-pressure switch located on the refrigerant canister next to the compressor. This should restore accurate pressure measurements.

Refrigerant Overcharge or Undercharge:

While low refrigerant levels might prevent the clutch from engaging, overcharging the system could lead to the compressor constantly running. Ensure the refrigerant levels are correct based on manufacturer specifications.

Solution: Check refrigerant levels using a pressure gauge. If it measures below 20 psi, refill the refrigerant to the recommended level, ensuring proper pressure for the switch to function correctly.

Compressor Leakage:

A leaking compressor can impact the system’s pressure, causing the low-pressure switch to maintain clutch engagement. Using a UV light to detect refrigerant leaks, indicated by a bright green glow, is a method to identify such compressor leaks.

Solution: Use a UV light to detect refrigerant leaks from the compressor. Repair or replace the leaking components to restore proper pressure levels.

Faulty Relays or Wiring:

The relay that controls the AC compressor clutch might be malfunctioning or stuck in a closed position, continuously sending power to engage the compressor clutch. 

Solution: Check the relay by swapping it out with a known working relay and see if the issue persists. Also, inspect the wiring for any shorts or damages.

Faulty Parts:

  • Faulty Thermostat: The thermostat may have failed or broken. 
  • Faulty Compressor: The compressor may have failed or broken.
  • Faulty Air Conditioner Heater: The heating element in the air conditioning may have failed, causing the AC not to work. 

Solution: The faulty parts need to be replaced. This can usually be fixed with a new element and a new thermostat.

Short Circuits or Electrical Faults:

A short circuit or electrical fault in the wiring, relay, or control system can lead to the constant engagement of the compressor.

Solution: Check for any wiring issues, shorts, or faulty relays. Ensure the relay isn’t stuck closed, replace if necessary, and inspect the wiring for any signs of damage or incorrect connections.

AC Compressor Clutch Always Engaged: General Troubleshoot

Your air conditioner clutch stays engaged even after the engine has been turned off, which is a common problem that can be a pain to fix. So to begin, it’s essential to know the difference between the A/C clutch and the engine clutch. 

The engine clutch disengages when you turn off your car, while the A/C clutch remains engaged to help your air conditioner maintain its adequate operating temperature.

Installing a manual override switch on your A/C system will allow you to disengage the A/C without turning off your car.

It is swapping out your vehicle’s original thermostat for a new one that has an override feature integrated into its design or repairing an electrical fault in one of your vehicle’s wiring harnesses. 

Try to focus on this process:

  • Diagnose the problem first before swapping out a thermostat or wiring harness. Then, try to start your car with the A/C engaged and turn off your vehicle again. If your A/C still finishes cooling after a few minutes, then it’s likely that other issues are causing this problem. If your engine still turns off after several minutes, then you’ll need to move on to the next step.
  • Start by taking note of everything in front of you. Then, look inside your vehicle at all of the various parts and systems that come into contact with the A/C system. 

Pay particular attention to any of these components. The A/C compressor relay monitors and switches power to the A/C compressor and the auxiliary air pump Relay monitors and switches power to your vehicle’s coolant temperature sensors.

Fans that move air through the system expansion valve on your A/C system heater blower relay change the relay from hot to cold depending on whether or not you have heat. 

AC Compressor Clutch Always Engaged
AC Compressor Clutch Always Engaged

Other Uncommon Reasons And Fixes For AC Compressor

There are a few uncommon causes as well that may result in the AC compressor always working. These are-

System Design:

Some modern AC systems are designed to keep the compressor engaged under specific conditions, such as high demand or certain temperature thresholds. This might be normal behavior for certain vehicle models or climates.

PCM (Powertrain Control Module):

Problems with the Powertrain Control Module (PCM) or control module may lead to incorrect signals instructing the compressor to remain engaged. Conduct diagnostics to check the PCM signals and ensure they’re correctly commanding the compressor. 

Reset or replace the PCM if necessary.

Blocked Drain Pan or Tank Hoses:

If your drain pan has both water and debris in it, it will cause the AC to work less efficiently. You can fix this by removing the drain pan and vacuuming up water and debris. 

If your tank has a riser hose, this will cause the problem. Again, you can fix this by changing the drain pan and riser hose.

Broken Fuse:

If this is the case, you will want to call an electrician to fix it. Again, this is because you cannot fix this yourself.

Defective Air Conditioner:

If you have a portable air conditioner, check out these tips on diagnosing and repairing it yourself.

Frequently Asked Questions (FAQs):

What Are The Signs Of A Broken AC Compressor Clutch?

Look for higher cabin temperatures, loud noises during compressor operation, or the clutch not moving when the AC is on.

How Long Should The Clutch of An AC Compressor Be Engaged?

A standard AC compressor clutch should engage and disengage about two to three times an hour, not staying engaged for more than twenty minutes at a stretch.

Is The Pulley of The AC Compressor Continually Spinning?

Yes, the compressor pulley should continuously spin to engage and pressurize freon; if it’s not spinning, a new belt may be needed.


So, when the AC compressor clutch stays on all the time, it could mean some problems, like the refrigerant freezing or issues with the compressor switch. It’s important to know how the AC system and clutch work and find out why it’s always engaged. You should get the help of a mechanic if you want the problem fixed properly.

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