FOR COOL HEADS: THE AIR CONDITIONING COMPRESSOR

The air conditioning compressor is the central element of the air conditioning system. This is because it compresses and transports the refrigerant through the refrigerant circuit of the air conditioning system. Here a distinction can be made between electrically and mechanically driven air conditioning compressors.

Air conditioning compressors are available in different designs, with the most common being swash plate compressors [1], scroll compressors [2], and vane compressors (rotary vane compressors) [3]. Swash plate compressors with pistons are generally used in passenger cars.

  • [1] Swash plate compressor
  • [2] Scroll compressor
  • [3] Vane compressor
  • [4] E-compressor

Purpose and function

In combustion engines, the air conditioning compressor is usually driven by the vehicle engine via a V-ribbed belt. The compressor sucks in the gaseous refrigerant coming out of the evaporator via the low-pressure lines, compresses it, and then transports it via the high-pressure line toward the air conditioning condenser. Hence its name, the compressor. During this process, the refrigerant is heated to a high temperature and forced into the air conditioning condenser under high pressure. This produces evaporation cooling for the cabin via the intermediate stations of the air conditioning condenser and evaporator.

Electric vehicles have to use electrically driven air conditioning compressors, because there is no longer a circumferential ribbed belt. But hybrid vehicles also benefit from electrically driven compressors since they can be operated according to demand, thus reducing fuel consumption and CO2 emissions. In vehicles that are fully or partially electrically driven, the air conditioning compressor also performs another important function. In these vehicles, the air conditioning system directly or indirectly cools key components of the powertrain: battery, traction motors, and power electronics. Keeping these components at the right temperature is vital for their service life as well as for the charging speed and range. The role of the air conditioning compressor is thus changing from a comfort component for cooling the cabin to a component of the powertrain.

Cross section of a swash plate compressor

1. Screw connections
2. Suction pressure valve
3. Cylinder head
4. Gasket
5. Piston
6. Swash plate
7. Driving shaft
8. Housing
9. Oil cap
10. Gear wheel

Most common causes of failure

If a customer comes to your workshop and tells you that the air conditioning system does not cool properly or no longer cools at all, you need to keep a cool head. That’s because there can be many causes of compressor damage. It’s therefore important to remember that you need to systematically search for the error and then fix it. The most common causes of failure are as follows:

  • Overheating due to loss of refrigerant oil
  • Seizing due to water ingress
  • Hydraulic shock due to overfilling with too much refrigerant or refrigerant oil
  • Foreign objects (e.g., chips) in the refrigerant circuit
  • Compressor damage after overheating
  • Connecting rod broken and deformed
  • Traces of overheating on the air conditioning compressor

Care and expertise are needed to avoid damage.

  • Regular maintenance
    We recommend performing an annual air conditioning check and an extended air conditioning service every two years.
  • The refrigerant circuit must be free of dirt, chips, and other foreign objects.
  • When replacing the compressor, the refrigerant circuit should always be flushed to remove contamination completely.
  • After any compressor damage, replace the filter-drier/accumulator, the expansion or throttle valve, and, if necessary, the air conditioning condenser.
  • Make sure that the refrigerant and oil filling quantities are in line with manufacturer specifications, check them when replacing the air conditioning compressor, and adjust them if necessary.

Keep cool! It´s time for the A/C check!

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