An air conditioning system in the car ensures pleasant temperatures during the warm summer months. If the expected cooling does not start even though the automatic air conditioning is switched on, the air conditioning compressor is often defective. Find out now which symptoms indicate a defect in the air-conditioning compressor and which causes are possible. We also tell you when a replacement or repair is worthwhile and how the air conditioning compressor is replaced.

How the air conditioner compressor works

As the central element of the air conditioning system, the air conditioning compressor compresses the refrigerant it contains. For this purpose, the compressor sucks in the gaseous refrigerant from the evaporator. During compression, the temperature of the refrigerant rises sharply. The refrigerant, which is now liquid and under high pressure, then enters the air-conditioning condenser, where heat is extracted and the refrigerant becomes gaseous. The refrigerant then returns to the evaporator via the expansion valve.

Various air conditioning compressors

Most air conditioning compressors are driven via the engine’s unit drive, whereby the compressor shaft is engaged via a magnetic clutch. There are also so-called clutchless air conditioning compressors. These models do not require a magnetic coupling. Purely electrically driven air conditioning compressors can also be found, depending on the vehicle model.

Defective air conditioning compressor – Replace or repair? 

When the air-conditioning compressor is defective, the question often arises: Replace or repair? Both approaches have advantages and disadvantages. Repairing the air conditioning compressor sometimes saves money, but replacing it is usually quicker. As a rule, it depends on the extent to which the compressor is damaged. However, removal is usually unavoidable.

Replacing the air conditioning compressor

It is particularly time-saving and reliable to replace a defective air conditioning compressor with a suitable spare part. For replacement, the defective air-conditioning compressor is removed and replaced with a suitable replacement part. However, a new part often incurs high costs. Especially for older vehicles, it can therefore be worthwhile to buy a used spare part.

Repair of the compressor by a professional

If the air conditioning compressor is broken, it can be sent to a specialist company for repair. Some companies specialize in the renewal and maintenance of parts of the air conditioning system, including the air conditioning compressor. Here, the air-conditioning compressor is subjected to an inspection, dismantled into its components and finally rebuild. 

Repairing the air conditioning compressor yourself

A defective air conditioning compressor can sometimes be easily repaired if only certain parts are affected. For example, the driver plate or the magnetic coupling may be damaged. A defective bearing or coil can also be replaced in some cases. Skilled car mechanics sometimes replace these parts themselves to save costs.

Symptoms of a defective air conditioning compressor

If the air conditioning compressor is defective, typical symptoms often point to the problem. If the air conditioning in the car does not work despite the correct setting of the automatic air conditioning, a defective air conditioning compressor is one of the most common reasons. In addition, the cooling capacity may be reduced in the event of a defect, and windows may mist up more frequently.

Error message or oil leakage

In modern cars, an error message can sometimes indicate a malfunction in the air conditioning system if the compressor is defective. However, a corresponding indication is not always stored in the fault memory. To ensure that the compressor is always well lubricated, it is filled with oil before installation. Oil leakage from the air conditioning compressor can be a sign of damage.

Air conditioning compressor makes noise

Another common symptom of a broken compressor can be unusual noises coming from the engine compartment of the car. These include loud and grinding noises that may indicate bearing damage or a seized compressor. Noises after starting may indicate lack of lubrication or dirt.

Overview of common symptoms of a defective air conditioning compressor:

• Air conditioner does not work
• Cooling capacity is reduced
• Car windows often mist up
• Error message in the error memory
• Noises when operating the air conditioner
• Oil leakage at the air conditioning compressor

Other components are also possible

Symptoms such as air conditioning failure or limited cooling are not always related to a defective air conditioning compressor. Other components of the air conditioning system can also be responsible for the problem. The condenser, the evaporator, a broken expansion valve or even missing refrigerant can also be possible sources of error.

Common causes of damage to the air conditioning compressor

If the air-conditioning compressor in the car is defective, there are various possible causes. Especially in older vehicles, progressive wear can be the reason for the defect. The air conditioning compressor wears out through friction and wear every time the air conditioning system is used. In addition, the compressor seals can harden.

Low usage and lack of maintenance

Not only frequent use of the air conditioner can lead to a defect, but also infrequent use. If the air conditioning system is not switched on for a long time, the air conditioning compressor is not lubricated regularly and can be damaged as a result. If the maintenance of the air conditioning system is neglected, damage to the air conditioning compressor can also occur.

Lack of lubrication and other problems

Lack of lubrication of the compressor often leads to its premature demise, for example caused by a low level of refrigerant or a leak. Damage to the air conditioning compressor can also occur as a result of other defects within the air conditioning system. Weather influences can also promote wear and tear and encourage a defect.

Overview of reasons for air conditioning compressor defects:

• Wear on the air conditioning compressor
• Seals are hardened
• Air conditioning is not used for long intervals 
• Refrigerant level too low
• Consequential damage due to other defects
• Lubrication is poor
• High loads due to weather influences 
• Air conditioning system was not maintained

Changing the air conditioning compressor

If the air conditioning compressor is broken, it is best to replace it completely with an intact compressor. Since the air conditioning system cannot be used with a defective compressor, the replacement should be carried out promptly. However, a thorough diagnosis of the problem should be carried out beforehand. This will ensure that other components – such as the air conditioning condenser – are not responsible for the failure. 

In order to be able to carry out the replacement of the compressor, appropriate specialist knowledge is required. In addition, the refrigerant must be extracted from the air conditioning system with a special device and disposed of in accordance with regulations. This is best done by a workshop with the appropriate equipment. The exact procedure for changing the compressor differs depending on the vehicle.

Changing the air conditioning compressor in 6 steps

1. Prepare replacement: The first step is to prepare for the compressor replacement. For this purpose, it is necessary to extract the refrigerant with a special device or have it extracted. This is a job for a specialist. Also, depending on the vehicle model, various attachments or parts in the engine compartment must be dismantled in order to have access to the air conditioning compressor.
2. Relax the V-belt: In the second step, the V-ribbed belt is slackened in order to be able to change the air conditioning compressor. In many engines, the belt tensioner can be released and fixed with a tool. The V-belt is then removed from the belt pulley on the air conditioning compressor. On some models, this is best done from below using a lifting platform.
3. Remove the air conditioning compressor: After removing the unit belt, the next step is to remove the defective air conditioning compressor. To do this, the connection lines of the air conditioning system must first be dismantled. This may cause some oil to leak out. At the same time, the electrical connections on the air conditioning compressor can also be removed. After loosening all the fastening screws, the air conditioning compressor can be removed from the car.
4. Prepare the new compressor: Once the removal of the old air conditioning compressor is complete, the new compressor can be prepared. It is often delivered with plugs on the connections, which must be removed before installation. In addition, the oil level in the compressor must be replenished according to the manufacturer’s specifications and with the specified oil.
5. Install the air conditioning compressor: The prepared compressor can be installed in the car in the next step. If possible, the seals of the connection lines should be replaced with new ones beforehand. Then the air-conditioning compressor is inserted into the engine compartment in reverse order, screwed tight and connected to all connections.
6. Complete the replacement: In the last step, the V-belt is tensioned and the replacement is completed. If the car is already older, it makes sense to replace the tensioning pulley and V-ribbed belt in this step at the same time. The air conditioning system can then be checked for leaks by a specialist and filled with the intended refrigerant.

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