Car air conditioning compressor (user:rde-groups CONTAINSANY 'XVIP_AMC_UK' AND user:rde-groups CONTAINSANY 'XHTW_Wholesaler')
Car air conditioning compressor
  • print
  • mail

Car air conditioning compressor

To make the subject of “Air Conditioning Compressors” more intelligible and to simplify the processes of inspecting and replacing them in the everyday work of an automotive garage, we show you here the construction and function of an air conditioning compressor, explain how to repair and replace it and supply hints for troubleshooting noise problems and performing the replacement. This technical video gives you practical information and demonstrates how to professionally exchange or replace the air conditioning compressor.


Important note:
The following technical information and practical tips were created by HELLA to support professional automotive garages in their daily work. The information presented here on this website should only be used by trained automotive technicians taking the respective safety regulations and country-specific legislation and practice into account.


Car air conditioning compressor: Overview and important instructions


The air conditioning compressor is driven by the vehicle engine via a ribbed or V-ribbed belt. It compresses and transports the refrigerant in the system. There are different types of compressor design.


The refrigerant is sucked in as a gas at low pressure and low temperature from the evaporator; it is then compressed and sent to the condenser as a gas at high temperature and high pressure.


Before installing a new compressor, you must check the oil quantity and the viscosity according to the manufacturer's instructions and refill as needed!


Effects of failure

A damaged or failed compressor can manifest itself as follows:
  • Leakage
  • Development of noise
  • Insufficient or no cooling performance
  • Error code in the air-conditioning control unit or engine / central control unit

There are a number of possible causes of failure:

  • Bearing damage caused by a defective tensioner or by wear
  • Leaks in the compressor shaft or the housing
  • Mechanical damage to the compressor housing
  • Contact (electrical connections)
  • Electrical control valve
  • Lack of refrigerant oil
  • Lack of refrigerant
  • Solids (e.g. swarf)
  • Humidity (corrosion etc.)
  • Defective tensioning elements and ancillary units


 Function test and pressure measurement of the system:

  • Does the compressor switch on, is the connector plug securely in place, is power applied?
  • Check the electrical control valve and/or the activation circuit.
  • Check that the drive belt is positioned correctly, undamaged, and that there is power.
  • Check visually for loss of sealing.
  • Check that refrigerant hoses are securely in place.
  • Compare the pressures on the high and low-pressure sides.
  • Read out the event memory in newer systems.
Air conditioning compressor Experience the air conditioning compressor now!

Experience the air conditioning compressor now!

Seeing means understanding - Discover the vast possibilities of our unique Know How Tool.


Practical and in detail, we show you:

  • components at work,
  • actively helping you identify the fault cause and
  • assisting in the repair process by providing you with technical background knowledge.


Take advantage of our Know How Tool and discover the unique experience of practicality made simple.


Start the Know How Tool now >


Note: Password protected area - Login needed!
The source of this content is the Online Portal for automotive garages HELLA TECH WORLD. To see the information login is required. The registration for the HELLA workshop portal is absolutely free of charge.

Click here and register now for free >




Car air conditioning compressor repair


Workflow for error analysis and replacement


Car air conditioning compressor replacement: Video

Video: Car air conditioning compressor replacement

Professional compressor replacement

Professional replacement of an A/C compressor in compliance with the manufacturer's installation instructions


04:43 min


Car air conditioning compressor damage



After correction of a leak or air conditioning service the air conditioning system does not function anymore. After the replacement of air conditioning components as well as after normal air conditioning service it happens from time to time that the air conditioning system does not function properly anymore - either immediately or shortly after the work conducted.


What is the customer complaining about?

The customer originally brings the vehicle into the garage claiming that "the air conditioning system does not cool properly anymore or "the air conditioning system does not cool at all anymore".


What does the garage do?

In such cases, the filling level of the refrigerant circuit is usually checked first.


It is often found that the refrigerant amount in the system is insufficient. Depending on the system type, up to 10 % of refrigerant can diffuse from the air conditioning system within one year.


However, before the system can be newly filled with refrigerant, it must be determined, whether the lack of refrigerant is caused by "natural loss" or a leak. If a leak is suspected, the system may not simply be filled with refrigerant again. First, a search for leaks must be performed, where the air conditioning system is e.g. filled with forming gas and tested using an electronic leak indicator. Depending on the result, either the leaking component (figure 1) of the refrigerant circuit is replaced, or the filter dryer element only. Next, the system is properly evacuated and filled with refrigerant and oil according to manufacturer's specifications.


When the air conditioning system is started up again, it may occur that the compressor output is gone. If the pressure values are compared at the service station it can be observed that the values on the high pressure and low pressure side are almost identical (figure 2). It can be suspected that either the flow in the refrigerant circuit is insufficient (e.g. at the expansion valve) or that the compressor is defective.



Strangely enough, there are cases, where the high pressure and low pressure values during the initial air conditioning system inspection are within the normal range, and merely the refrigerant filling level is too low; and where problems only occur after proper new filling of the air conditioning system.


Evacuating and new filling can loosen dirt particles or metal abrasion, which can then deposit in the control valve (figure 3) of the compressor or in the expansion valve/ orifice tube (figure 4) and cause malfunctions. This can particularly occur if the filter dryer was aged or the system was "under-filled".


What needs to be done?

In the case of problems the compressor should be removed and the oil should be drained.


If a "greyish discoloration" (grey-green or grey-yellow if dye is used) of the oil can be detected, where fine metal particles (figure 5) are present as well, the refrigerant circuit must be properly flushed due to the foreign particles, the expansion valve and the filter dryer must be replaced, and the refrigerant circuit must be evacuated according to the specifications and newly filled with refrigerant and oil. After that, the system should function again without problems.


Is the customer sufficiently informed?

As the garage provided the customer merely with an estimate for the search for leaks and possibly for replacing the leaking component or the air conditioning service only, they may face arguments with the customer. The customer is often not ready to pay for the significant additional costs for e.g. replacing the compressor or flushing the system. For this reason, a detailed discussion with the customer, where the technical issue and risks are presented, is especially important.


What is the cause for the compressor failure?

The compressor contains the only moving components of the refrigerant circuit, and must respectively be sufficiently supplied with oil. Another task of oil in the refrigerant circuit is compressor cooling in order to avoid overheating.


If a compressor is operated with an insufficient amount of refrigerant for an extended period of time (e.g. due to a leak), this results in insufficient heat dissipation and lubrication of the compressor components, as the oil must be transported together with the refrigerant through the air conditioning system. Due to the excessive operating stress on the compressor components, metal abrasion is generated on the components, which may cause partial or complete blockage of the control valve located on the inside. The control valve blockage results in the compressor not properly working anymore. This damage can only be corrected by professional replacement of the compressor, which also includes flushing of the system. By the way, insufficient lubrication results in damage in all compressor designs. However, power controlled compressors react particularly sensitively to insufficient refrigerant and/or oil.


Information for garages and parties accepting repairs

If the customer brings a vehicle for repair due to insufficient cooling capacity, he should be informed about a possibly required replacement of the compressor.


The reason for that is that a possibly insufficient refrigerant quantity and the related lack of lubrication can cause pre-existing damage. In the case of doubt, the compressor must always be removed. If the oil is contaminated, the system must be flushed prior to replacing the compressor.


If the customer request a deviating approach, the garage should record this on the bill and/or to have the customer confirm his request in writing. This Technical Information was prepared in collaboration with compressor manufacturer Sanden and is applicable to all compressor manufacturers and compressor types currently known in the market.




Air conditioning compressor noise: Troubleshooting information in the case of noise


The following information should always be taken into consideration when troubleshooting noise sources and prior to every compressor replacement:


Check all retaining clamps and attachment points for breakage or cracks and possibly missing bolts or nuts.
Any vibration caused may be the cause of excessive compressor noise. Observe, whether the noise changes, if you e.g. apply force onto the retaining brackets or attachment points using the assembly lever (figure 6). If a change occurs, the noises are most likely not caused by the compressor.


Check tubes and pipes to determine, whether vibrations from the engine or pulsing refrigerant enter into the vehicle interior.
For this purpose, hold them with one hand and observe possible changes in the noise (figure 7).


Check V-belts, tensioners, tension pulleys, freewheel clutch (alternator) and belt pulleys for smooth running, play and alignment.
Excessive tolerances caused be worn parts can cause noise.


Excessive high pressure (figure 8) can cause abnormal compressor noise.
If the high pressure service connection is additionally located behind a blockage in the system, the high pressure may even be higher than indicated on the manometer. In order to diagnose such a problem it is useful to measure the temperatures at the compressor.


Excess or contaminated refrigerant causes excessive high pressure, which may cause compressor noise.
The same applies to refrigerant, where the content of non condensable gases (air) is too high.


The condenser can also be considered as cause of unusual noise.
If insufficient air is routed through the condenser, the refrigerant cannot sufficiently condensate and the high pressure increases excessively. This can result in abnormal noise development. Check as well, whether the fan(s) transport(s) sufficient air through the condenser. Check the condenser and radiator fins for possible contaminations as well (figure 9).


Often noise can be caused by contaminated expansion valves (figure 10) or orifice tubes.
This can e.g. by caused by contaminations in the form of metal abrasion. This causes a reduction of the refrigerant flow and excessive high pressure occurs. "Defective" expansion valves can e.g. generate diverse "buzzing, whistling or droning noise", which can be well perceived in the vehicle interior.