Step By Step Guide To Fix AC System Of Your Car

Diagnosing AC Compressor Failure

During summer, a trip under the scorching heat from the sun can only be made less miserable with the use of air conditioning. But broken air conditioning in your car can entail an excruciating time for a drive. At the heart of the car’s AC system lies the AC compressor which on failing will disrupt the working of the entire AC system in your car. 

The air compressor is responsible for compressing the freon or refrigerant gas to circulate across the system. If the compressor fails, the system ceases to receive freon which stops the supply of cool air into the cabin. If you are experiencing air conditioning troubles then start by checking your air compressor and its related parts for failure. 

How to diagnose AC Compressor Failure?

The air compressor is the central unit of the air conditioning system and ensuring its proper functioning is essential for optimum performance. The vehicle’s AC compressor sustains huge pressures and heat along with constant wear and tear which, like every other mechanical component in the vehicle, can fail as well. 

Check Cabin Air

The first sign of potential air compressor failure is hot air blowing from the AC vents. The freon is pressurized and pushed throughout the system with the help of the compressor and so if it fails, the AC system will not work properly. However, there are many other reasons for hot air blowing like low refrigerant, excess oil, clogged condenser, defective thermal expansion valve, etc. Make sure to properly diagnose the air compressor before replacing it with a new one.

Check Compressor Drive Belt Condition

The drive belt commonly known as the serpentine belt is what drives the compressor using the engine’s power. This belt is connected to the crankshaft and spins on the compressor pulley. So if the serpentine belt is faulty then the compressor won’t get any power and hence won’t run which means the AC in your cabin won’t function. Excess slack in the belt can cause slippage or can be too loose to even engage the pulley. Slack can be easily adjusted by tightening the bolt to the tensioner. But if the belt is torn, frayed, or worse then replacing it is necessary. Also if the belt tensioner cannot hold and apply steady pressure on the belt, then it may also need to be replaced. 

Check Clutch Engagement

The next step is to check whether the compressor is being driven when the AC is switched on. The compressor is not in constant engagement with the engine, instead, it is operated when the compressor clutch is actuated that drives the compressor shaft. Most modern cars have an electromagnetic clutch which is part of the compressor pulley assembly. The clutch consists of a drive plate, pulley, bearing, and stationary coil. When 12v is applied to the coil, an emf is applied to the clutch drive plate which causes it to engage with the driven pulley. The clutch plate is directly splined or connected to the compressor shaft. So when the clutch is engaged with the pulley, the compressor shaft starts rotating, and therefore the compressor runs. 

The clutch and pulley assembly are often the failure point in the system and hence must be checked for proper functioning. To see if your clutch is engaging with the pulley you can open your hood and locate your air compressor. The front part of the pulley is the clutch drive plate. When the engine is running and the AC is switched off, you can see that this plate remains stationary but the pulley rotates with the belt. Now if you switch on the AC from the cabin, you should notice the plate starts moving with the pulley. Note that the compressor is directly controlled by the ECU which may intermittently stop and start the compressor based on its heat and the pressure in the system. So if you notice the clutch plate starts and stops after short spans, don’t be alarmed as it is simply the ECU maintaining optimal compressor performance. 

The clutch can go bad for various reasons like a bad relay, fuse, wiring issue, detective coil, or worn-out clutch friction surface. If the clutch does not engage then there can be an electrical issue that needs to be sorted. A simple way to check the electrical system is to apply 12v directly from the battery to the stationary coil or the clutch lead wire. Do this with the engine turned off If the clutch does not move then the problem is most likely the coil and if it does move, then the issue is with the electrical system: fuse, relay, wiring, switch or control module.

Lastly, check the air gap between the clutch and the pulley because if the clearance is improper, the clutch can not engage at all or slip and run against the pulley causing excessive wear and heat which leads to clutch plate failure. To check the gap, you can use a feeler gauge. Every compressor has different specs so you will have to refer to a service manual for the correct gap. Commonly the gap should be within 0.015 to 0.040-inch press fit clearance.

Check For Unusual Noises

If your clutch is successfully engaging and disengaging periodically, then you don’t have clutch-related issues. With the engine and AC running at max, open the hood and listen for any unusual sounds like clunking, grinding and squealing noises coming from the compressor and pulley assembly. A grinding noise could indicate the pulley or internal compressor bearing is faulty. A broken pulley bearing can be easily replaced but internal compressor bearings warrant a compressor replacement. A leaking bearing will also cause squealing noises to emanate from the compressor. A clunking noise indicates that the compressor has broken and the metallic debris in the compressor is slashing around causing an unsettling clunking noise. In this case, the only solution is to replace the compressor unit. The squealing noise can also be due to excessive belt tension. Try relieving the stress on the belt by loosening the tensioner assembly.

If you suspect that the pulley bearing is toast then you can verify that by checking for play in the pulley assembly. With the assembly attached to the compressor, try rocking the pulley back and forth, and If it wobbles or rocks then the problem lies in the pulley bearing. Replacing the pulley assembly is doable since they are sold separately from the compressor unit. It is also a good idea to swap out the clutch plate while you’re at it to futureproof the compressor. 

Check For Leaks

The most obvious cause of compressor failure is leakage in the system or the compressor itself. A leakage causes the freon to deplete from the system. Now since the compressor’s lubrication oil is part of the freon itself; low freon means low lubrication oil which causes the compressor to run dry, experience excessive heat, wear and tear and eventually seize or break. If your refrigerant level is too low then the AC in your car won’t work and the compressor will fail eventually which is why it is important to check, find and fix the leak in the AC system. 

There are various methods of scoping out leaking freon such as using UV dyes and special UV flashlights for leak detection, ultrasonic sound detection, or an electronic leak detector. The common leakage points or vulnerable areas where leaks are typically found are the AC line connection gaskets and seals, condenser, compressor connections or the compressor shaft seals, the condenser unit, etc. If you find a leak between connections then the issue may simply be a bad seal or O-ring in the AC system. A leak in the compressor can be a serious problem and will require a complete compressor rebuild or replacement. 

If your air compressor is not working for any of the above factors then having it fixed is necessary to restore your vehicle’s air conditioning system. The air compressor is vital to the AC system functioning and maintains pressure and refrigerant circulation throughout the system and any irregularities in compressor functioning will directly affect the entire system. Most air compressors last a fairly long time if maintained properly with regular inspection and refrigerant and oil refills. Other components like the compressor clutch, pulley assembly, and drive belt need to be maintained and periodically checked for optimal performance. A bad clutch or pulley bearing will eventually do irreparable damage to the compressor and cause more expensive fixes. So make sure that the compressor and all its components are working efficiently for prolonged AC compressor life.


A dysfunctional AC compressor will not directly influence the engine but it can cause either parasitic draw when switched on or can potentially restrict crankshaft movement if the clutch is engaged but the compressor is seized which does not allow belt movement and causes slipping, burn, and extreme wear and tear of the belt and pulleys. Although most modern AC systems have sensors that disengage the compressor if the system pressure is too high, the freon level is too low, or if the compressor is unsuitably high in temperature.

Replacing the compressor is a relatively complicated task as it requires the AC system refrigerant to be flushed completely before taking out the compressor. However, you can replace the compressor yourself if you properly remove the refrigerant by either taking it to a shop or flushing the system yourself. Once the AC lines are empty you can remove the compressor. Make sure to refill the appropriate refrigerant and the right type of lubrication oil for the compressor.

You can drive a car with a bad AC compressor but you will not be able to operate the air conditioning in the cabin which can result in an uncomfortable ride. It is important to make sure the compressor belt and pulley operate freely without any noises or wobble or it may affect the other belt-driven accessories or even the engine.

Like all machines, the compressor requires lubrication to work smoothly and efficiently. This lubricant is usually provided by the refrigerant. So a lack of refrigerant in the system or a lack of oil in the refrigerant can cause the compressor to run dry and fail. It can also fail due to excess pressure and heat or if the refrigerant is contaminated in any way.

The life of the AC compressor depends on a few factors like the specific vehicle and its age, type of AC usage, and servicing regularity. Typically the AC compressor can last about 8- 10 years with proper maintenance.

John Framigllia
Technical Writer
Our technical writer is known for simplifying automotive parts and services. Intuitive with various vehicles and manufacturers, he knows how to simplify complicated problems.