If an AC compressor clutch doesn’t engage, the problem could be caused by the fuse, the wiring, coil, ground, pressure switch lockout, or even the engine coolant temperature switch.
The clutch and compressor are essential parts of your car’s AC system. Therefore, proper maintenance of both is vital if you want your system to work well. Keep reading to learn why the AC clutch is not engaging and how to fix the issue.
How to tell if your AC clutch has engaged
To determine whether your AC clutch is engaging, you have to set the AC settings in your car cabin to the max with the engine idling.
Pay attention to the engine RPM and load. You should hear and feel the engine behave like it has taken on an extra load. This will be denoted by a change engine sound and a slight fluctuation on the RPMs that you can see on the tachometer.
You can also confirm by visually inspecting the AC compressor under the hood. Identify it (the location varies from vehicle to vehicle but it is driven by a belt.) If the AC clutch and the pulley are spinning, it means that it’s okay. However, if it’s only the pulley that’s rotating, the system has an issue. It could be any of those discussed in the previous sector of this article.
Before proceeding to the next step, you should understand a couple of things. Some cars use a digital input from the thermostat to turn on the AC clutch, while others use a pressure switch to figure out the operating conditions of the cooling system before engaging the clutch.
Ensure to check the entire system carefully to identify the problem quickly. Follow these steps:
- Remove the connector cable from the clutch coil. This allows you to examine the power and ground more better.
- Measure the battery voltage and the ground using a digital voltmeter at the removed connector. Ensure the AC is at max mode.
- If you cannot read the voltage results, examine the AC relay fuse using a multimeter.
- If the fuse is okay, examine the clutch relay.
- Always ensure the AC compressor has enough oil at all times. Insufficient amounts can also cause the AC clutch to fail.
- If no battery voltage reaches the connector, pull the compressor clutch relay to check for ground and power on the relay control coil terminals.
What tells the AC clutch to engage?
Once you turn the AC on, it energizes the clutch. This engages the armature plate and compressor belt of the compressor drive, causing the compressor drive to rotate along with the car engine.
When you turn off the AC, the AC clutch is de-energized. This disengages the armature plate and compressor belt of the compressor drive. The AC compressor clutch is part of the car AC system designed to engage and disengage the AC compressor pulley from the compressor drive. Typically, you operate it through an electromagnetic switch.
The clutch consists of a friction plate next to an electromagnetic coil, which, when engaged, the current moves through this coil, creating an electromagnetic force. This force pulls the coil towards the friction plate, giving the pump rotor power to keep the compressor running.
Reasons AC clutch is not engaging and fixes?
Below are several of the most common causes of a faulty AC clutch;
Blown AC Clutch Fuse
An AC compressor clutch fuse can cause a clutch to not turn on or engage. First, you have to find the cause of the fuse’s failure. This can come from a shorted hot wire or faulty clutch assembly.
To determine whether the fuse is working or not:
- Turn the car engine off
- Remove the fuse from the fuse box.
- Use a multimeter to check whether it’s still functional
- If the fuse is okay, the cause of your AC clutch not working is something else.
- Put the fuse back into the system.
AC Clutch Relay Failure
Most vehicles rely upon a relay to control AC clutch operation. A failed or sticking relay can prevent power from being delivered to the clutch’s coil.
Faulty Switches
Modern automotive AC systems rely on several switches to operate efficiently. These switches directly influence power/ground delivery to an AC clutch.
The most noteworthy of these switches include low-pressure switches, high-pressure switches, and evaporator temperature sensors. The failure of any of these sensors can render an AC clutch inoperable.
Faulty Wiring
An AC compressor’s clutch assembly is provided power and ground through a wiring pigtail that departs from an engine’s main wiring harness in most cases.
The compressor’s clutch will not operate if an open condition exists on any wires within this circuit. As a result, the compressor’s clutch will not operate. The wiring may be fine in some cases, but the harness is the problem.
Low Refrigerant Charge
An AC system’s low-pressure switch is designed to cut power/ground delivery to the compressor clutch in the case of low system pressure. Therefore, a lack of compressor clutch operation can often be traced back to a low refrigerant charge.
High Refrigerant Charge
Likewise, an AC system’s high-pressure switch is designed to cut power/ground delivery to a compressor’s clutch in an over-pressurization event.
If a system were to be overcharged with refrigerant, the high-pressure switch would naturally disable clutch operation.
Faulty AC Clutch
A compressor’s clutch assembly can begin to show its age with time. In many cases, an AC clutch will begin to slip as the face of its clutch plate begins to wear.
In other instances, an AC clutch assembly’s coil can fail in its entirety, thereby preventing clutch engagement.
Control Head/Computer Failure
An AC clutch receives its operational commands through inputs made by a driver through the system’s dash-mounted control head. Therefore, failure of any type within this unit can prevent a clutch’s coil from being energized.
Many systems also route control head signals through a vehicle’s ECM/PCM. Because of this, partial failure of a control module can also lead to a compressor clutch in operation.
Clutch Sensor-Default Lockout
Most modern cars feature AC clutches that use low and high-pressure switches and compressor oil levels to turn on and off. Possible reasons why your clutch won’t engage, especially after detection by the sensor, include:
- Low refrigerant.
- Excess refrigerant
- Insufficient oil
Damaged Ground Wire
The foundation for the electrical wire operation is the ground. Therefore, damaged or bad ground means the electrical currents cannot find their way to the battery. In this case, the clutch won’t engage. Signs of damaged ground include your car lights flickering randomly.
Leaking Evaporator Coil
The evaporator coil is a car AC element in the cabin that helps blow the air to cool the car down. A broken or leaking evaporator coil is detectable by a hissing sound or foul odor upon turning the heat and AC. This causes the clutch not to engage.
Worn/Damaged Clutch Plate
The auto AC system needs electricity to function. So, when the electromagnetic features overheat or get damaged, the AC clutch may break down. Also, the clutch plate wears over time, causing the AC clutch to fail or slip.
Other Causes of AC Clutch Not Engaging
- Broken AC expansion valve.
- Broken driver/receiver
- Clogged condenser
- Improperly set compressor clutch air gap
Potential fixes
The solution will depend on the particular cause of the problem.
First, add more coolant to your system. Remember, the AC system features various pressure switches that open and close based on the refrigerant levels in the system. Too much or too low of the refrigerant will result in the clutch disengaging.
Get yourself a repair kit to help you recharge your refrigerant. But if the level is too low and cannot engage the AC clutch, a DIY kit may not recharge it. Never charge the system forcibly. If the coolant level is too low, use the Freon coolant or octane booster. You may also have to replace the evaporator coil.
If all the components are functional, check whether the compressor clutch has worn out and replace it. If you notice any leakage in your car’s system, have it checked as soon as possible. It helps avoid moisture and air coming in.
Note: when moisture combines with the refrigerant, it will create acid and sludge. This condition can damage the AC system.
How To Manually Engage AC Compressor Clutch: The Easiest Methods
If you’ve done tests repeatedly only for them to go wrong, and you cannot manually engage the AC compressor clutch, you may have to jump-start the AC compressor clutch manually.
To do this, connect the clutch’s wire to the battery directly. The AC should blow cool air, and the clutch will engage. In this case, the problem could be due to a faulty relay or pressure switch.
Here are several methods you can use to force the AC clutch to engage,
Add More Coolant
What is the most common reason for an air conditioning compressor not to engage? Low level of refrigerant. When the coolant level in the system goes down, the low-pressure switch does not allow the compressor to rotate.
How to manually engage the AC compressor clutch when the system is low on antifreeze? Easy. Just adding refrigerant will solve this problem. If your car is compatible with the R134a type of refrigerant, attaching a can to the system will override the low-pressure switch and restore the normal function of the compressor clutch.
Note: When you manually engage the compressor, make sure that the system has enough oil. Inadequate lubrication can damage the compressor.
Jump-start The Clutch
The process is slightly different for older cars that are not compatible with the R134a type. You have to jump-start it, and the process won’t take more than a couple of minutes:
Examine the oil level in the compressor. Add oil if the level is below the normal point. Check the owner’s manual to check the correct instructions for checking up the compressor oil and level and filling it up.
Unplug the single wire connector on the front side of the compressor. Next, take the fused jumper wire and connect its one end to that side of the wire connector connected to the compressor.
Attach the other end of the jumper wire to the battery’s positive terminal. It will supply the battery voltage to the compressor clutch, allowing it to engage manually. Again, there is no need to switch on the air conditioning system for this method to work.
Note: You should route the jumper wire to avoid tangling or interfering with other moving components.
Replace The Clutch
When the clutch engages, but the compressor does not spin, it is time to replace the clutch. A bad AC compressor clutch needs immediate fixing. A delay can cause serious damage to the air conditioning system and the engine. Changing the compressor clutch could be the only solution in this case.