Why the right oil matters in A/C compressors

Why the right oil matters in A/C compressors

DENSO Aftermarket’s Senior Technical Engineer Gerard Magielsen reveals why the wrong A/C Compressor oil is the biggest cause of product failure – and offers an essential A/C checklist

99.9% of all compressor problems stem from a poor understanding of A/C system operation, maintenance and repair say DENSO, one of the world’s leading suppliers of A/C compressors for automotive applications.

DENSO now supply a new compressor installation guide with every DENSO Compressor sold. But there is one aspect in particular that causes the majority of avoidable A/C Compressor problems: the oil.

Universal oil: a key cause of compressor failure

Compressors are vital to a vehicle’s A/C system; compressing the low temperature, low pressure gaseous refrigerant from the evaporator, into a high temperature, high pressure gaseous refrigerant, and discharging it to the condenser.

Oil in the A/C system is essential, primarily to lubricate moving parts including the compressor and the expansion valve needle. It also enables heat to escape from the compressor. As with refrigerant, oil in the A/C system must retain its chemical stability.

Insufficient lubrication due to universal oil is the second most frequent reason for A/C compressor damage and failure. Analysis of DENSO A/C Compressor warranty claims for 2012 showed that in 24% of cases, garages did not use the correct PAG-oil needed for DENSO A/C Compressors.

What are the pitfalls of universal oil?

The use of incorrect oils, such as universal oils or oil mixtures, inevitably leads to A/C compressor damage. This is because universal oils, often preferred by garages, are PAO-oils, or mineral oils with a different viscosity than synthetic PAG-oils. The difference between these two types of oil means that they do not mix, leading to poor lubrication, damaged seals and increased wear.

If the oil is diluted, the lubricant base layer decreases.  This results in the piston rubbing against the cylinder bearing surface. If the oil is too thick, it is unable to ‘squeeze’ between the cylinder and the piston.  DENSO’s First Time Fit® quality A/C Compressors have a tight tolerance between cylinder and piston of only 3 μm. A change in the oil viscosity can result in more frictional resistance, leading to an increase in compressor temperature and subsequent seizure.

Blending or mixing of different types of oils may lead to the formation of paraffin.  This can block the flow of the refrigerant and oil, leading to seizure of the compressor and system failure.

Quantity as important as quality

DENSO also advise that the quantity of oil in the system is of great importance. Too little oil leads to poor lubrication of the compressor, rising component temperature and oil scorching on the suction side of the compressor. Too much oil in the system will increase the load on the piston-crank system, which can lead to a block in the body of the thrust bearing and the hard front piston co-pivotable skid plate.

Is the oil filtered?
It is also essential that any solid impurities in the compressor oil are removed in the filter-dryer. The filter-dryer will also capture moisture from the oil. As part of the annual maintenance of the A/C system, it is equally vital to remove a proportion of the oil, replacing it with the same quantity of fresh oil.

DENSO recommends
To ensure the longevity of your DENSO A/C Compressor, DENSO always advises technicians to refer to the type label and only charge the compressor with refrigerator oil that is of the specified quality and viscosity. Any warranty claim received after use of other oils or mixtures will not be accepted.

Other essential A/C checks
As well as checking that the A/C system is properly filled with correct amount and type of refrigerant and oil, garages and workshops must make several other regular checks:

  • Check the pressure and temperature of the exhaust before and after the compressor
  • Check the temperature of the cables from the compressor and the condenser. High pressure should be hot and dry
  • Check the cleanliness of the condenser and radiator fan. The appearance of moisture or frost on the high pressure side could mean a blockage in the flow of refrigerant
  • Check the temperature difference before and after the dryer.  A difference of more than 3°C indicates too much moisture
  • Check the refrigerant flow, ice on any element of the air conditioning system is due to a blockage
  • Check the tension and condition of the compressor belt
  • Check for any unusual noises from the compressor, expansion valve, fans, blowers and air-conditioning ducts

DENSO’s A/C Compressor range
The extensive DENSO A/C Compressor range includes Reciprocating type (swash plate type) and Rotary type (Vane Type and Scroll type) as well as an Electric compressor for hybrid vehicles (Scroll type). They are all 100% original equipment quality: guaranteed fit, right first time with 450 part numbers covering over 2,500 applications.

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