If your A/C compressor clutch won’t engage, it might be due to other damaged components. However, power is supplied to the A/C compressor clutch’s magnetic coil when your vehicle’s A/C system needs to be turned on.
When the clutch coil is energized, it moves the clutch drive plate towards the clutch body and compressor pulley, engaging the clutch, and creating a magnetic field for better engagement.
The A/C compressor clutch transfers all the rotational energy created by the engine’s serpentine belt to the compressor driveshaft when it is “on” or “engaged.”
In contrast, if the vehicle’s A/C system is turned off, the associated clutch coil is de-energized. Thus, the A/C system clutch disengages. If the air conditioning system has little refrigerant, its clutch might engage and disengage repeatedly.
However, in this article, you’ll be provided with a few reasons for your A/C compressor clutch not engaging. You’ll also learn and understand what the clutch is designed to do, how to diagnose it, and possible repairs to it.
What is the AC compressor clutch meant to do?
The air conditioning compressor clutch is a part of the automobile A/C system that engages and disengages the compressor pulley from the compressor drive.
Typically, it will be controlled via a magnetic switch. The clutch engages when the A/C is turned on, supplying power to engage the armature plate of the compressor drive and, consequently, the belt that engages the compressor drive.
The clutch itself has a friction plate and an electromagnetic coil. When the A/C is turned on and the clutch is engaged, electrical current flows through the electromagnetic coil and creates electromagnetic force.
This force transmits power to the pump rotor, producing a gripping action that pulls the coil toward the friction plate and maintains the compressor and its functions of producing cold air.
When you turn the A/C off, the clutch has no electrical power. The absence of power allows the armature plate of the compressor drive to disengage from the compressor belt, and the compressor clutch simply disengages.
What Causes the AC Compressor Clutch Not To Engage?
Here are some of the things that could be causing the AC compressor clutch not to engage:
#1. incorrect amount of refrigerant.
The air conditioning system requires the correct amount of refrigerant to operate. The problem could be caused by too little refrigerant or too much refrigerant in the system.
A modern system works by utilizing an AC pressure switch lockout to safeguard the valuable components in case there is too much or too little refrigerant.
The power will be shut off to the AC compressor clutch and thus the clutch will not engage if the pressure in the AC system is either too high or too low on either the low pressure side or high pressure side.
If the AC pressure is too high, you or someone else may have overfilled the AC refrigerant system. If the pressure is too low there is most definitely a leak in the AC system.
#2. Damaged or Worn Clutch.
The AC compressor clutch may have simply worn out and requires replacement (like any other clutch). This is more typical of older cars or cars that have had excessive use of their air conditioning.
With newer clutches, generally they won’t wear out. If the clutch plate wears out, the clutch will fail to engage at all.
In some cases, it may engage, but then it will slip, and the operations will be inconsistent. Certain AC clutches have spacer shims that can be removed to obtain a little more life from the clutch. It may also be a failed clutch coil, in which case the clutch coil will fail to engage at all.
#3. Failed high or low AC pressure switch.
Your AC compressor clutch might not be engaging because of a faulty high or low AC pressure switch.
The AC system has two AC pressure switches: one on the high-pressure side and another on the low-pressure side. These switches internally regulate AC pressure in the system and keep it from being too high or too low.
Even if the pressure is read as acceptable, a misbehaving switch may be reading the pressure wrong and causing the AC compressor clutch to shut off.
#4. Bad electrical connection.
Your car’s AC system has quite a few electrical connections and wiring; if there is a problem with any of them, the clutch may cease functioning.
However, the most critical connection is the 12V+ power wire to the AC clutch; if this wire is damaged or corroded in any way, the clutch will not engage.
#5. Blown Fuse.
A blown fuse could also result in an AC compressor clutch that won’t engage. If the electrical system of the AC is shorted, the compressor could get too much voltage which will blow the fuse in that operation.
It is better for your AC system to blow a fuse than get too much voltage. If you got too much voltage, you could be damaging your external, expensive AC system components. The fuse for the AC compressor is in the owner’s manual.
#6. The faulty or leaking evaporator coil.
The evaporator coil works with the car’s air conditioning to create airflow for cooling the car. So if the coil is faulty or leaking, it could prevent the AC compressor clutch from engaging.
If you hear hissing or there is an odor, the evaporator coil is faulty or leaking when heat and air conditioning is switched on. The clutch would not engage.
You might need to replace the evaporator coil. But just remember, $ is involved in replacing something!
How to diagnose why your AC compressor clutch isn’t engaging
Start by turning your A/C settings in the car all the way up to see if your AC clutch is working. Next, turn the engine on and look under your hood where the air conditioner compressor is located. If AC clutch and the pulley are both spinning, it is safe to say that everything is fine.
If the pulley spins but not the clutch there is a fault in the system, and one of the causes above may apply.
Examine the belt that covers the compressor pulley. If the belt is worn down or slipping you may want to replace it or tighten. Make sure to check for rust around the clutch plate and if you see any it is likely to be caused by an old worn out compressor that may be broken.
Check the wiring to the clutch, the wires could be improperly or loosely connected and affecting the operation of the compressor. The wires must be connected and in good condition to supply enough power to the clutch.
(The evaporator temperature sensor, and high-pressure switch could also be broken or have bad wiring.) The fuses for your AC compressor can be found in the fuse box. If you find a blown fuse it’s simple to replace.
How to fix an AC compressor clutch that fails to engage?
Ways to fix the failed AC compressor clutch:
Check refrigerant levels and adjust them
It’s best to start with this, because it’s usually the most common fault with automotive air conditioning systems, either too low or too high a level of refrigerant. To see if it’s too little or too much refrigerant, you can use dedicated gauges to test if the levels are right.
In either case, the clutch may not disengage. You can add refrigerant gas to the correct levels using a DIY repair kit. But we do recommend that this be completed professionally with the proper equipment.
Measure the voltage transferred to the AC clutch
The simplest way to check a problem with the AC clutch is to measure the voltage going to the clutch coil.
With most cars, the AC connector has a +12 volt wire that is connected to the vehicle’s electrical system; sometimes you will also have a ground wire. The process is simple: start the engine, turn on the AC, and remove the AC clutch connector.
If everything is functioning properly, you should measure 12 – 14 volts when measuring the voltage being delivered to this wire with a multimeter. If there is a ground wire, you will want to measure that as well.
If you get the proper voltage and ground, you have determined the problem lies with a defective AC clutch, clutch coil, or corrosion in the connector. If there is no voltage, you have to proceed with troubleshooting.
Check the low and high AC Pressure Switches
Next, check the high and low pressure switches of the AC system. Usually, you can electronically measure them using a multimeter.
However, you’ll have to have a repair manual for your car model to know what values to expect or at what points in the circuit should be open or closed.
For some newer cars, you can scan the AC system using an OBD2 scanner and display the pressures that these sensors are measuring using an appropriate diagnostic tool.
Jump-start the clutch
You can jump-start the clutch to check if it will engage manually, but do not try this until you are completely sure you understand this, as if you do it wrong, you could damage a valuable item.
Follow a wiring diagram to ensure you have the correct wire. You will just connect the clutch wire directly to the battery.
If this does not work to engage the clutch, you will need to install a new clutch. However, installing a new AC compressor is usually the better choice. If you engage the clutch manually, you may have some other more rare problems.
You may need to repair an electrical connection, replace a blown fuse, or replace a pressure switch instead.
Inspect the electrical connections
Another issue that could cause the AC clutch not to engage is a confusion of connections or faults with the wires, as mentioned above. Connections need to be checked, as the AC clutch needs an electrical connection in order to engage correctly.
Checking the power wire to the AC clutch is generally where you start troubleshooting the system; if power is not being provided to the clutch, it will not engage.
In addition to this connection, the remainder of the wires in the system should be visually inspected. Perceive/make note of any wire or connector that is damaged and replace it immediately.
Check for any blown fuses and replace
You will first need to identify the correct fuse for the system before you will be able to check the fuse. There should be a diagram in the service manual for your car. With the engine off, do the following:
You can now use your multimeter to verify the fuse operation, once you identify the correct fuse. If it is blown, you can only replace it.
If you find that the fuse continues to blow, then there could be a more serious electrical problem going on. And be sure to replace the fuse with the proper amperage.
How Much Does An AC Compressor Clutch Replacement Cost?
When replacing an air conditioning compressor clutch, putting in a whole new compressor is typically the best bet. When the clutch goes bad, chances are the rest of the compressor will fail shortly thereafter, so for the cost, it’s just not worth messing around with the clutch.
The cost to replace an AC compressor ranges from $650-$1,400. Parts cost somewhere between $400-$900, and the labor makes up the rest, which is generally 2-3 hours for the replacement. Your overall repair cost depends not only on the vehicle you drive but where you get the work done. Labor costs vary greatly by state, with California being the highest and Ohio being the lowest.
Even in that state, the region will make a difference. If you go to a small engine mechanic in a rural area, you will likely pay much less than you would at a busy urban mechanic.
Of course, the least expensive way to replace the AC compressor is to do the job yourself, although unless you’re mechanically inclined, it would be difficult to perform. I’m not saying you have to be on a professional level like I am, but you do need to know how to work on the air conditioning system, along with some special tools.
In order to replace the AC compressor, you would need the proper AC tools to drain the AC system and refill it, so in a case like this, you may just want a professional to perform the work properly and with the right equipment to make a safe replacement.
Is it worth it to replace the AC compressor clutch?
No. Concerns with customers I’ve had over replacing the AC compressor clutch, is that your mechanic most likely will not do this, replacing the compressor is the better decision.
The AC compressor is pretty old at this point and unless you like dealing with problems, they’re almost always better off replacing the whole compressor unit. You will spend a bit more, but you will get a little less anxiety.
Can I Drive my Car with a Bad AC Compressor Clutch?
You can probably drive your car, but you will want to repair it sooner than later. If it has seized, it could cause your serpentine belt to get damaged or your AC system.
If you have a serpentine belt failure, both the alternator and water pump would stop function, which would lead to a more serious concern.
What Would Burn Out an AC Compressor Clutch?
You may simply replace the AC relay or AC pressure switches; they are both parts responsible for supplying the power to the clutch and the compressor directly. If the relay is malfunctioning, it could send wrong power to your compressor clutch and this would in turn burn it out.
How long do AC compressor clutches last?
The average life of a car air conditioning compressor is generally 10 to 12 years. The clutch is a moving part and takes a good bit of abuse. The clutch will fail before the compressor would bust over time, but you will most likely just replace the whole unit instead of the clutch individually.
If you plan on staying cool this summer, it would be better to leave your car AC system working. Nothing worse than showing up to work all sticky with sweat; so, if all signs point to the AC compressor clutch is broke, you will want that repaired, unless you are kind of like sweating.
If you are not familiar with working on the car’s air conditioning, speak to a professional. This system is very sophisticated and not meant for a novice mechanic.