FrigAir and Sanden give you some suggestions for the maintenance of your compressors.
The core of the automotive A/C is the refrigerant circuit. Within this cycle, the heat from the cabin is exchanged with the ambient, transported by the refrigerant (e.g. R134a). The components of a standard refrigerant cycle are compressor, condenser, expansion valve and evaporator. The compressor is the heart of the vehicles’ air conditioning system; it is a very delicate component, the principal source of disruption in the A/C structure.
The compressor is sucking in the refrigerant in a gas state with a low pressure. After compressing it up to a higher pressure, the hot gas is pumped into the condenser. At this stage the refrigerant exchanges the heat with the ambient and cools down nearly to ambient temperature, the pressure is still high. At the Thermostatic expansion valve the refrigerant expands, pressure and temperatures goes down. The cold refrigerant is now passing the evaporator and exchanging the heat with the hot cabin air.
The compressor is driven by a belt attached to the vehicle’s engine which is engaged by an electromagnetic clutch called the compressor clutch. The A/C compressor is activated by the electronic clutch. When the a/c is switched on a drum inside the belt pulley is magnetized attracting and locking the belt drive into place making it so that only when engaged does it add extra resistance.
In the A/C system, the performances of one component affect the performances of the rest, due to his delicate components when the A/C system fails, the first part that is suspicious is the compressor, and so it is the first part replaced. From Sanden’s experience: 30% of compressors replaced during warranty period are without any problem; more than 65% are broken due to reasons not liable to compressor; and less than 5% fail due to a compressor production defect. Wrong diagnosis and wrong repairs cause high cost to all involved parties.
The main enemies of the compressor are hits, dirtiness and bad refrigerant/oil circulation.
It is obvious that hits to the car can cause serious damages to the compressor. Hits can break the ears or the armature of the compressor and they can affect the right functioning of the pulley, causing noises and a general wrong functioning of the compressor.
The refrigerant pumped from the compressor to the condenser must be without impurities, so it’s really important to have cleaned filters to prevent a lack of performances or damages to the system. Remember to flush the system after a compressor failure, because it could be contaminated with particles that can cause severe damage to the valves and subsequently to the right functioning of the compressor.
REFRIGERANT/OIL WRONG CIRCULATION
If we have conditions under which there is not a proper circulation of oil or refrigerant, the compressor internal parts will not be refrigerated or/and lubricated, and so the internal parts will be damaged.
The typical causes for wrong circulations of oil refrigerant are:
- Wrong amounts of oil/refrigerant. It is important to adjust the oil/refrigerant amounts to the one specified by the A.C. system manufacturer. In case of too small amounts of oil/refrigerant, the internal compressor parts will not be refrigerated/lubricated, and so the compressor will fail. The most difficult situation comes when a vehicle have had a crash and we do not know the amount of oil lost. In such cases the best option is to do a flushing of the system and put the oil amount recommended by the A.C. system manufacturer.
- If any part of the system have a lock, the oil/refrigerant circulation will not be correct. Special attention must be given to the receiver drier, which has to be replaced after a compressor replacement, expansion valve proper functioning and any other filters of the system as the one of the calibrated orifice.
- In the case of a small leak, the refrigerant amount will be decreasing in a slow way. It is thought that the compressor is protected from leaks by the pressure sensor. Pressure sensor protects the compressor in the case of a quick leak (Eg.: condenser broken in a crash), but it does not protect the compressors in case of a slow leak.
An expert mechanic must checks all the symptoms before changing the compressor, so before proceed with the wrong procedures you need to make right diagnosis, to help you with this process the compressor oil aspect is an excellent tool that can tell us what is happening with the compressor without disassembling it.
Clear yellow colour is the aspect of an oil in normal conditions
Light grey colour is common in compressors that have run during a short time (very new compressors) due to the surface treatment of compressor internal parts. Later on during the A.C. running the oil turns to normal colour.
Green colour indicates the presence of additives to detect leaks. As there are many additives in the market, Sanden cannot guarantee the behavior of the compressor when additives are added to oil.
Orange colour indicates the presence of humidity. The origin is due to poor vacuum, or components contaminated by water. A proper clean of the system and replacement of the received drier is required before proceeding to charge the A.C. system with refrigerant.
Dark grey indicates the presence of very small metal particles inside the oil. The origin is due to compressor wear/seizure as consequence of wrong oil/refrigerant circulation.
Silver colour indicates the presence of medium size metal particles inside the oil. The origin is due to compressor internal damage, due to compressor defect or wrong working conditions, such as a liquid compression that creates abnormal efforts. The compressor must be replaced. A proper clean of the system and replacement of the received drier+ expansion device is needed before proceeding to charge the A.C. system with refrigerant.
There are other several problems concerning the compressor:
Remember that the warranty on compressors will only be granted for defects caused during the manufacturing process. Furthermore, FrigAir warranties will not be awarded unless the following procedures carried out:
Did we check leak, clean the system, put a new receiver drier, verified replace the TXV?
(source: Sanden “Compressor failure root causes”)