If you live in a hot country, you know the importance of having a functional A/C system in your car.
Unfortunately, the AC system contains many different parts, which means that many parts can possibly fail.
But how do you know if the AC compressor is the one to blame when your AC system is not blowing cold air anymore? Let’s find out!
Symptoms of a Bad AC Compressor
- AC System blows warm air
- Noise From AC Compressor
- Compressor Clutch is not moving
- Burned rubber smell from the engine bay
- Auxiliary Drive Belt Excessively Wearing
- Refrigerant Leak
Here is a more detailed list of the most common symptoms of a bad AC compressor.
A/C System Blows warm air
This may seem like an obvious first choice on the list. However, there are a number of things to look out for, which could point to a bad compressor being at fault if your A/C stops working.
If your vehicle indicates that your A/C should be on (usually by a little light on the A/C button), but you don’t feel a temperature change, this could point towards a faulty compressor.
A good way to check if your compressor is the fault here is to check your A/C compressor’s power feed. The compressor will usually have a 2-pin connector situated on the exterior of the body. As the vehicle is running and the A/C is switched on, you should have a live feed going to the pump.
If your compressor has the correct feeds to it but still isn’t working, this would suggest a faulty A/C compressor.
Noise From AC Compressor
As you can imagine, when the compressor’s clutch is engaged, the internals of the pump are working incredibly hard to keep up with the demand.
Once the bearings and other metallic components start to wear and become noisy inside the compressor, you will usually begin to notice a harsh grinding noise coming from the engine.
A good way to determine if it’s your compressor that’s making this noise is to try switching your A/C on and off and listen out for any changes in the grinding noise.
If you notice that the noise disappears when the pump is switched off, this would indicate that your compressor’s internals has worn and will require the unit to be replaced.
Compressor Clutch is not moving
Most ac compressors’ pulleys consist of two parts. The inner pulley will spin at all times with the engine without turning the axle into the compressor. It also has an outer clutch on this pulley which is engaged when the AC compressor should start.
If this clutch has failed, it will not engage and turn the compressor axle. No electrical power can also cause this to the compressor, so it needs to be diagnosed properly.
This is more a sign of a bad ac compressor clutch rather than a bad ac compressor, though. However, if the ac compressor clutch is bad, you often have to replace the compressor.
Newer cars mostly use variable AC compressors, which means they spin all the time and do not have this clutch.
Burning Rubber smell from the engine bay
If you notice a burning rubber smell from the engine bay when you try to turn on the AC, it can mean that the AC compressor is seized and that the serpentine belt will spin on the ac compressor pulley.
This will cause the serpentine belt to snap off quite quickly, though, so if you have been noticing it for a long time, there is most likely something else that is the problem with your car.
Auxiliary Drive Belt Excessively Wearing
If you’ve had to replace your auxiliary drive belt recently, and have noticed that your new one has started to wear out quite quickly, or is making a squealing noise, then it may be worth checking your A/C compressor’s pulley.
As your compressor’s pulley begins to wear out, it can develop excessive movement in its bearings that cause the pulley to run at varying angles. This movement will often cause snatching and grabbing of the rubber auxiliary drive belt and cause it to wear out prematurely. Or this excessive movement can give off a high pitch squeal as the rubber belt rubs against the now unaligned pulley.
To determine if this is your fault, remove the auxiliary drive belt from the A/C compressor and physically check the pulley for any excessive free play. Some compressors allow their pulleys to be changed without replacing the whole unit; unfortunately, this is rarely the case, and a worn pulley will often mean replacing the compressor itself.
Your vehicle’s A/C system has sensors in place to determine how much refrigerant there is within the pipework. If your vehicle develops a leak on one of these pipes and loses its refrigerant, your lower pressure switch will detect this and stop your compressor from running to not damage it from running dry.
A refrigerant leak on a vehicle can often be difficult to find due to the inaccessibility of the components that you’re trying to assess. However, a good place to start if you’re looking for a leak is the compressor body itself.
If the compressor has begun to over compress the refrigerant due to a fault internally, this can cause excessive heat and pressure to build up within the compressor’s body and can cause its seals to burst. Thus releasing its refrigerant and causing your A/C to stop working.
The Function of an AC Compressor
Your vehicle’s Air Conditioning compressor is really the beating heart of your vehicle’s A/C system. It’s basically a mini compressor that’s usually driven by your auxiliary drive belt. As your engine turns over, your auxiliary drive belt takes up power from your crankshaft and outputs this to your A/C compressor’s pulley.
Now, because not everyone runs their A/C 100% of the time they’re driving, your A/C compressor has a clutch fitted in the pulley. This clutch will engage and disengage the compressor as you switch your air conditioning on and off. So, if your A/C is switched off, then the pulley on the compressor will spin without turning the internals of the compressor itself.
When cooling, the A/C compressor is designed to increase the refrigerant’s pressure and temperature within the system. By tightly packing the gas-based refrigerant molecules allow the heat that the refrigerant has picked up from your evaporator to be released as it reaches your vehicle’s condenser.
AC Compressor Location
Your A/C compressor will usually be located somewhere on the auxiliary drive belt. It will have 2 refrigerant pipes connected to the body of it and an electrical plug to provide power.
The AC compressors are usually located towards the bottom of the engine, below your alternator and power steering pump, so you may check from underneath your vehicle to see the compressor.
AC Compressor Replacement Cost
An AC Compressor costs 200$ to 700$. Labor costs 200$ to 500$. You can expect a total cost of 400$ to 1200$ for an AC compressor replacement.
The AC compressor itself is quite a complex part, and therefore it can cost a lot to buy a new one.
The labor costs are often around 100$ for just the AC compressor replacement, depending on the car model.
However, after the AC compressor replacement, the AC system needs to be refilled, and this procedure usually costs 100$ to 200$. Before refilling the AC system, you also need to do a leak test on the system, which can take a long time and, therefore, the labor costs a lot.
Learn more: How Much Does an AC Recharge Cost?
The cost to replace your A/C compressor will vary greatly depending on how accessible it is to change, what refrigerant your vehicle uses as well as what type of compressor is fitted.
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Founder, owner & main author of Mechanic Base. I have been repairing cars for more than 10 years, specialized in advanced diagnostics & troubleshooting. I have also been a drifting driver and mechanic for over 7 years.