Compressor Oil - topping up and adjusting for R12

Too much oil gives poor cooling. Too little oil damages the compressor. When repairing leaks, or changing any components, the compressor oil must be topped up. The quantity of oil for each component depends on whether the leakage was slow or quick. Use mineral oil for the R12 system.

The A/C system is filled with 135 ml of compressor oil. A certain amount of compressor oil is always lost when draining refrigerant and replacing components. This amount must be recharged so that the operation of the system will not be adversely affected.

R12 systems use mineral oil.

Compressor oil should be topped up through the compressor oil plug.

The table below shows how much compressor oil is lost in connection with various types of work on the A/C system.

Reason for loss of oil Amount of oil lost
Draining refrigerant 20 ml
Burst A/C hose 30 ml
Replacement of hose 15 ml
Replacement of condenser 30 ml
Replacement of evaporator 30 ml
Replacement of desiccant container 20 ml
Replacement of expansion valve 15 ml
Replacement of compressor* 60 ml*

*Note that the new compressor is filled with 135 ml of oil before delivery. In order not to have too much oil in the A/C system, and so impaired cooling, oil must be drained from the compressor before it is installed. How much will depend on the amount of oil that has been lost in connection with the replacement of other components, if any. The A/C system should always contain 135 ml of compressor oil.

If only the compressor is being changed, 75 ml of oil should be drained from the new compressor (135 - 60 = 75). If, for example, the desiccant container is also being changed, only 20 ml of oil should be drained from the compressor, as per the following example:

135 ml (in a new compressor)
-20 ml (lost during draining)
-20 ml (lost when changing the desiccant container)
-60 ml lost when changing the compressor)
=35 ml (to be drained from the new compressor)