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w203 ac compressor

Diagnosing A/C Compressor Clutch Problems on your Mercedes-Benz

w203 ac compressorThe A/C system on your Mercedes-Benz includes many sensors and components including the air conditioner compressor. The A/C compressor is the heart of the system. One crucial element of the A/C compressor is the clutch.  It is important to understand how to check if the A/C compressor is engaging or not.  

Purpose of the A/C Compressor Clutch

While the A/C compressor on your Mercedes-Benz is an important part of the system,  the A/C compressor clutch is even more important. Every time you want cold air to blow on your Mercedes-Benz cabin you turn on the climate control and set your desired temperature. The Air Conditioner control unit starts gathering input from an array of sensors on your Mercedes-Benz.

When you turn on the A/C, the clutch engages and the pistons start to compress the refrigerant.

If no problems are detected such as low refrigerant in the system, it sends a signal to disengage the A/C compressor clutch. Otherwise the A/C compressor engages and starts to compresses the refrigerant. By compressing the refrigerant we add pressure to the system. The A/C compressor clutch engages to create the high pressure in the refrigerant and it’s state is controlled by the Air Conditioner Control Unit. If there are error codes on the A/C Control Unit the compressor will not engage and you will need to reset the fault codes using a diagnostic scanner such as the Launch Creader or iCarsoft MB II.

Test if the A/C compressor clutch is engaging

How to tell if your air conditioner AC compressor clutch is working / engaging? This video is helpful if you are trying to troubleshoot air conditioner problems, the A/C compressor clutch in particular.

  1. Start by turning the engine on. Set the AC to maximum cold setting.
  2. Open the hood and look at the serpentine belt to locate the AC compressor.
  3. Now look at the pulley of the air conditioner compressor. The center part (the clutch) should be engaged and should be spining along with the pulley.

The center part on the pulley of the A/C compressor will not spin when you have the air conditioner off or if there is a problem. Once you turn on the AC the center part of the compressor,  the AC clutch should engage and start to rotate with the pulley. The serpentine belt rides the A/C compressor pulley every time the engine runs, but the A/C compressor is working only when the A/C clutch engages it.

Clutch-Less Variable Displacement AC Compressor

Mercedes-Benz has started using clutchless variable displacement A/C compressor on many late models. A clutch less variable displacement A/C compressor can be found on models such as  W203 C-CLass and W211 E-Class. You will not be able to check the operation of the A/C compressor clutch on such compressors because there isn’t one. The following video explains how the clutchless variable displacement A/C compressors work.

Why your air conditioner clutch doesn’t engage?

When the A/C system does not blow cold air the first thing that you show check is if the compressor engages. If it doesn’t do not assume that the A/C compressor itself is the problem. Remember that the A/C clutch is controlled by the A/C Control Unit. If that unit detects an error it will not engage the A/C compressor to avoid it getting damaged. One other reason why the A/C compressor does not engage is the fact that the system may be low on R134 refrigerant. Typically older cars may have very slow leaks that may require top off with refrigerant every couple of years. You can use a R134a recharge kit to recharge your system if the A/C compressor is not working. Here are a couple of highly rated kits that you will find on Amazon.

Common A/C Compressor Clutch Problems


Possible Diagnosis

Possible Solutions

Blowing Warm Air

Suction pressure is too high

Discharge pressure is too low

Compressor delivers inconsistent pressure to the refrigerant

Addition of a shim to close air gaps between the hub and pulley

Replace A/C compressor clutch

Not Working

If A/C compressor has voltage, probably defective compressor clutch

Replace A/C compressor clutch


A/C compressor clutch coil receiving inadequate voltage

Overheating of internal winding

Slippage of hub against the pulley

Replace A/C compressor clutch

Noisy System

A/C compressor clutch may have a defective pulley bearing

Replace pulley bearing

Where to buy A/C compressor Clutch for Mercedes-Benz?ac compressor clutch test diagnose

Two of the best places online where you can buy new or used air conditioner compressor or clutch are listed below. If you know of any other resources please feel free to let us know.


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