Making compressor complications simple to understand

27 March 2018 | Article

Leading OE supplier helps workshops spot the signs of compressor faults and their causes in time for the Spring servicing peak.

Compressor Cutaway _Art

With Spring in motion, more and more drivers will be switching on their air-conditioning systems expecting a breath of fresh air.

However, after months of non-use, many will be greeted by the unpleasant surprise of a failed compressor which is often down to the wrong type of refrigerant being used.

A condensor is the main heat exchanger within the air conditioning system. It condenses the refrigerant in the air conditioning cycle into a liquid by exchanging the heat from the high temperature and high pressure gaseous refrigerant to the cooler outside air.

When it comes to the compressor, using the correct type of refrigerant is crucial to the air-conditioning system functioning properly, and recent legislation changes have meant that even the most experienced technician can make a mistake if they’re not clued in.

Ac -compressor -garage

To clear up many of these regular problems, DENSO outlines some of the most frequent compressor faults, and what their causes could be:

1. Clear separation of two different oil substances: one transparent and the other not

Clear Seperation Of Liquid

The problem: No variable displacement, system blockage or compressor seizure.

The cause of the failure will be the PA0 oil added to the refrigerant cycle. PAG oil and PA0 oil do not mix and will result in the creation of paraffin like substance.

Resulting in: The clogging of the control valve and the refrigerant cycle.


2. Rubber seals are swollen and do not fit in the original position

Rubber Seals Swollen

Problem description: No variable displacement and system leakage.

Cause of failure:  The system was filled with the wrong type of refrigerant. It could also be due to the incorrect additives (conditioners) or flushing agents being used.

Resulting in: The refrigerant, oil, additive or flushing agent swelling the compressor rubber seals.


3. Clear separation of two different liquids: one is forming droplets on the other

Clear Seperation Of Liquids Forming Droplets

Problem description: Excessive noise and compressor seizure.

Cause of failure: The POE oil added to the refrigerant cycle. PAG oil and POE oil do not mix properly.

Resulting in: A high percentage of POE will reduce lubrication performance.


4. Discharge port is black and discoloured

Disharge Port Black And Discoloured

A hardened or a gel like substance inside the oil or suctions port

Problem description: No variable displacement, system blockage or compressor seizure.

Cause of failure: Leak stop additive or conditioner added to the refrigerant cycle.

Resulting in: Chemical reaction of the leak stop or conditioner caused blockage of the compressor control valve and / or expansion valve.


5. Cracked or shattered plastic pulley

Cracked Or Shattered Pulley

Problem description: Drive belt noise or drive belt disengaged.

Cause: Incorrect removal or installation of the drive belt.

Hitting the DL-pulley before or after installation.

Resulting in: Excessive force was applied to the pulley resulting in cracks or shattering of the pulley.

Compressor Range _1 (1)

Since 2017 every car manufactured will be using use the new refrigerant R1234yf in the air conditioning system, as the industry attempts to make the systems more environmentally friendly.

Each compressor will need a specific ND oil to prevent any failures, also depending on whether it’s using the new R1234yf refrigerant or R134a, so it is always worth checking the manufacturer’s instructions which details exactly what each compressor will need.

To help workshops, DENSO provides a wide range of A/C Compressors to workshops which are new, filled with the corresponding oil types and delivered as complete assemblies.

Find out more

Further details of DENSO’s product range are available online at, on TecDoc or from your local DENSO Aftermarket sales contact.

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