Inside Line: Denso

DENSO---Fitting-AC-compressorTechincal expert Alan Povey explains diagnosing A/C faults on the Ford Fiesta. Two of the most common indicators are abnormal sounds and emissions.

Listen in

The sounds made by the air con unit can help you pinpoint a host of issues.  The table below shows how to identify a range of problems by simply listening to the noise of the air conditioning system.

Once the source of the noise has been identified it is important to know what action to take:


Cause: Mechanical rattling due to internal wear. The abnormal wear is due to the non-circulation of oil (poor lubrication) caused by a lack of gas in the system

Corrective Action: Repair with a new or remanufactured compressor of the same type

Blaring and Roaring

Cause: Internal damage due to excessive belt tension and water intrusion into bearings

Corrective Action: Replace only the rotor

Woo Goo

Cause: Pressure of refrigerant fluctuating causing vibrations through the discharge pipe and condenser

Corrective Action: Put rubber bush in piping clamp to put down noise, or replace the pipe/hose with one equipped with a muffler

Clinking and Crunching

Cause: Possible causes of loud operating noise are down to a large gap between the hub and rotor or rough hub and rotor friction surfaces.

Corrective Action: Determine if the noise is due to normal operation or is excessively high.  If excessively high, check the gap and adjust as necessary.  Aiming at the lower limit will reduce the operating noise.


Cause: Low belt tension

Corrective Action: Measure tension with a tension gauge and adjust as necessary

Cause: Oil on belt

Corrective Action: Check belt for oil and replace if necessary

Cause: Misalignment

Corrective Action: Re-adjust alignment

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- who has written 1202 posts on CAT Magazine.

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