Air Conditioning Compressor

Back to: WIS 83.40 Automatic Climate Control (ACC) or Heating Ventilation and Air Conditioning (HVAC)

Description - Air Conditioning Compressor

The W220 uses a Variable Displacement Compressor (A9) in which the volume is varied between 2% (minimum stroke value) and 100% (maximum stroke value) by the externally controlled A/C compressor valve.

The appropriate Pulse Width Modulated (PWM) signal is sent to the compressor control valve via the ACC push-button control module, depending on the refrigeration requirements.

The refrigeration requirement is determined primarily by the temperature settings for the vehicle's passenger compartment and the values measured by the in-car temperature sensors.

The following will affect the PWM signal sent to the compressor control valve.

• Selected temperatures on the ACC Pushbutton Control Module (N22),
• In-car temperature sensors,
• Humidity,
• Sun intensity,
• Outside temperature,
• Evaporator temperature, and the
• Engine coolant temperature.

Description - Air Conditioning Drive Pulley

The W220 Air Conditioning Drive Pulley which couples the compressor to the Serpentine Belt does not employ an electro-magnetic clutch. Instead the compressor rotates continuously at a speed similar to the engine RPM and the quantity of cooling achieved is determined by the setting of the variable displacement in the compressor.

In the event of a compressor failure which causes the compressor to seize, the Air Conditioning Drive Pulley is designed with a rubber coupling element between the drive pulley grooves and the compressor crankshaft which can distort or even fracture thus decoupling the compressor from the engine drive.

Issues - Air Conditioning Drive Pulley

When the AC compressor starts rattling and it's not cooling inside the cabin, the clutch (Air Conditioning Drive Pulley) may have gone bad and needs to be replaced. If you continue to drive it with a faulty Air Conditioning Drive Pulley it may shred your Serpentine Belt or v-belt and damage other components.

It is possible to diagnose a faulty Air Conditioning Drive Pulley by listening for unusual noises with a mechanic's stethoscope. This is a very useful tool, and is available cheaply from places like Harbor Freight, or from virtually any large auto parts store.

Replacing - Air Conditioning Compressor

If the AC compressor needs to be replaced, the filter dryer must also be replaced as a matter of course. While the system is being repaired it is also a good idea to replace the expansion valve.

The compressor is DENSO, and is available on Amazon and is not too expensive.

Location - Air Conditioner Filter Dryer

TBD

Resetting - Air Conditioner

If the R134 fluid is low or lost, the compressor throttling valve and swash plate will be disabled by the car's computer. The control system then has to be reset. Note you cannot recharge the air conditioner until it has been reset.

Regular car A/C shops usually don't know how to service M-B Automatic Climate Controls (ACC), as they don't have the STAR DAS equipment, and they don't know how to access the Automatic Climate Control (ACC) Service Menus.