Although modern A/C compressors in cars are fairly robust and therefore reasonably reliable, modern A/C compressors are also subjected to extreme operating conditions that include high under-hood temperatures, huge temperature swings, constant vibration, and occasionally suboptimal lubrication. Thus, since all of the above conditions, either individually or collectively, can severely reduce the useful service life of an A/C compressor, these components may need replacement at least once during the average lifespan of a modern vehicle.
Function Of A/C Compressors
When an automotive A/C system is in operation, the function of the A/C compressor is to pressurize the refrigerant gas in the A/C system. Next, the refrigerant enters the condenser, which is a heat exchanger that cools the pressurized gas refrigerant to the point where the gas becomes a liquid. From here, the cooled liquid refrigerant moves into a component called the evaporator. Here, the liquid refrigerant evaporates as air entering your cabin flows over the evaporator (it should be noted that the evaporator is extremely cold thanks to the refrigerant). The air flowing past the evaporator heats the refrigerant (thereby cooling the air flowing into your cabin), after which the refrigerant is filtered in the accumulator and returned to the compressor. Once the refrigerant returns to the A/C compressor, the cycle starts over.
In practice, most A/C systems are designed to have variable duty cycles, which means that the compressor does not run all the time even though it is driven by the engine with a drive belt. In order to accomplish variable duty cycles, most A/C compressors are fitted with electro-magnetic clutches that can disengage the compressor. In a fully functional automotive A/C system, the compressor clutch will remain engaged until either the cabin temperature reaches its pre-set level and is automatically deactivated, or the A/C system is deactivated manually by the driver. Automatic climate control systems will continuously activate and deactivate the compressor in order to keep the interior temperature constant at the set level.
Common Symptoms Of Faulty A/C Compressors
The most common symptoms of faulty A/C compressors can be similar to the symptoms caused by the failure of other components in the A/C system. As such, it’s important to do your due diligence to ensure that the compressor is the faulty part before commencing work. That said, a faulty A/C compressor could cause the following symptoms:
Poor Cooling In Cabin
If the compressor is at fault, it is usually because internal components are broken, damaged, or worn to the point where the refrigerant cannot be compressed sufficiently. Note though that if the compressor’s clutch is worn or if sufficient current does not reach the clutch, the clutch can slip. If this happens, the compressor may rotate too slowly to compress the refrigerant effectively. The result is that you’re A/C blows hot air.
In some cases, excessive mechanical wear of internal components can cause grinding, whining, or other mechanical noises both when the clutch is engaged and disengaged. This is typically heard when you’re A/C compressor is running.
Broken Drive Belt
Some mechanical failures, such as bearing failures, can cause the A/C compressor to lock up. When this happens, there is potential to cause the drive belt to snap. Note that when this happens at high engine speeds, other components such as the radiator, radiator hoses, radiator fans, and wiring can be destroyed by the flailing ends of the broken belt. If the A/C compressor shares a drive belt with the water pump, your car could also quickly overheat.
Replacing A/C Compressors
Before attempting repair, it should be noted that the A/C system refrigerant MUST be purged with proper equipment, and charging of the system must similarly be performed with proper equipment to prevent over or undercharging of the system, both of which can cause premature failure of the replacement compressor and/or other system components. Additionally, proper equipment is necessary to mitigate safety and environmental risks.
It should also be noted that advanced refrigerants such as R-134yf are now used in place of R-134a on many modern A/C systems. Be aware also that unlike R-134a, R-134yf is flammable, which poses a significant fire risk, and that the two refrigerants are NOT interchangeable, mainly because of the fact that the two refrigerants require different lubrication oil formulations to keep the compressor properly lubricated.
Note: The example steps below are intended for general informational purposes solely to help give you an idea of project difficulty and tools required. As all cars are engineered differently, repair procedures and safety hazards vary from vehicle to vehicle. To ensure that you have a vehicle specific repair procedure and an exhaustive list of potential safety hazards, we advise you reference a factory service manual for your vehicle. Similarly, referencing a repair manual such as Chilton or Haynes might serve as a less expensive alternative.
Step 1 – As most DIY mechanics don’t have the necessary A/C purging and recharging equipment, we are going to exclude these steps from the scope of this article. If you do not have access to proper equipment, a local mechanic who does should perform this step for you. A mechanic can also confirm that you’re A/C compressor is faulty, as well as identify leaks or other faulty components in the system.
Step 2 – Once your system has been safely purged of refrigerant, you can remove the compressor. First you must remove the drive belt. This will require removal of tension on the tensioner. Depending on the type of tensioner, this can often be accomplished with a deep socket and a breaker bar. For some vehicles you may need a special vehicle-specific tool. Next, you’ll need to locate the compressor. Once you have found it, you will need to remove the hoses. This can usually be accomplished with a set of flare nut wrenches. Finally, you’ll need to remove the compressor from its mounting bracket. This can usually be done with ratcheting wrenches or a socket set.
Step 3 – Installing the new compressor can be accomplished by reversing the order of the removal steps. The same tools can be used. This is also a good time to replace any seals to prevent future leaks, including gaskets and O-rings.
Step 4 – Once the new compressor is installed, the system must be recharged with refrigerant. Again, unless you have proper equipment, we recommend having a professional mechanic complete this step to avoid possible safety and environmental risks.
Best A/C Compressor Brands
Denso is one of the largest manufacturers and suppliers of new A/C compressors to the OEM market. As such, Denso replacement compressors conform to OEM specifications in many cases, which ensures that regardless of what you drive, Denso can supply a compressor that was specifically designed for your application. Overall, they make high quality compressors and we are confident that if you choose to use one as a replacement, it will serve you well.
Unlike most other suppliers of both new and remanufactured A/C compressors, Four Seasons uses advanced vacuum and leak testing methods on each individual unit. Moreover, each Four Seasons compressor is tested under simulated real-world conditions that equate to 100,000 miles of actual use, which ensures that a replacement compressor supplied by Four Seasons should provide similar performance to an OEM unit. Four Seasons nicely blends high quality with affordable cost, making them a high value proposition next time you need to replace an A/C compressor.