Compressor oil: all you need to know

The most common error made during installation and servicing, improper compressor oil, is the most avoidable. DENSO explains how to avoid these simple yet costly errors.
Compressor Graphic Landscape

Compressor oil lubricates and cools the moving parts of the compressor and forms a film between cylinder and pistons. The oil therefore should have the correct lubrication performance, viscosity and miscibility with refrigerant.

The compressor acts as the heart for the A/C system; performing a critical role whereby, if the compressor stops working, the Air Conditioning system will fail too. When faults with compressors occur, they can be costly and labour-intensive to rectify. Knowing the common causes of compressor failure should therefore be of vital importance to garages and installers.

Beware of Universal Oil

  • DENSOs A/C compressor warranty claims show that in a quarter of all cases garages did not use the correct PAG-oil. The use of incorrect oils, such as universal oils or oil mixtures, inevitably leads to seizure and damage, and is the second most common reason for A/C compressor failure.
    • Universal oils, often preferred by garages, are PAO-oils with a different lubrication performance, viscosity and low miscibility with refrigerant to that of synthetic PAG-oils. Different viscosities cause a thinner oil film to form between the cylinder and piston, the low miscibility with refrigerant causes insufficient circulation of oil therefore reducing lubrication and cooling of the compressor. This will likely lead to compressor seizure and definitely will reduce the life expectancy of the compressor.

To identify the correct oil type, always refer to the compressor identification label - either attached to the rear or side of the compressor. The new label will also display the amount of oil inside the new compressor. In some cases this can be differ from the vehicle specifications so always check car manufacturer data.

Ensure the correct amount of oil is used

The amount of oil necessary for a typical system depends on type of compressor and system design and is measured to meet this combination. Both too much or insufficient oil will reduce life time of compressor and influence system cooling performance.

  1. After recovery of refrigerant: When removing refrigerant, some compressor oil will be mixed with the refrigerant and will be removed from the refrigerant circuit together with the refrigerant. It is essential that this oil is drained off at the A/C service station and its volume measured precisely. The volume drained need to be charged to the refrigerant cycle when refilling with refrigerant.
  2. After removal of the old compressor: Drain the oil from the compressor and measure the amount. Check the compressor installation guide for the appropriate oil drain procedure.

Installation tips:

AC Compressor Packaging
  • If the system has been flushed with refrigerant: Original DENSO Compressors which are delivered with the correct amount of oil can be installed directly. Turn the compressor systematically by hand to distribute oil evenly. This will avoid damage when the compressor starts moving or during start-up.
  • For some applications it is necessary to add oil: For example, where there is one and the same part number for Single and Dual evaporator cycles or when the oil quantity of the new compressor differs from the vehicle specifications. Always check the car manufacturer data to confirm the correct oil amount. Never add oil directly into the compressor, but instead to the condenser, receiver dryer or second evaporator cycle.

Holding a 40% share of the global market for original equipment A/C Compressors, DENSO is the world leader in the market. DENSO’s aftermarket compressor range is 100% OE with a guaranteed fit, “right first time”; providing consistent levels of air conditioning even when the vehicle is stationery, making the cabin air more comfortable.

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