Refrigeration oil - topping up and adjusting for R134a

The A/C system is filled with 200 ml of compressor oil. A certain amount of compressor oil is always lost in connection when draining refrigerant and replacing components. This amount must be recharged so that the operation of the system will not be adversely affected.

Systems with R134a use P.A.G. oil, part number 40 74 787.

Charging compressor oil should be carried out on the compressor's high-pressure side. Compressor oil is supplied in tubes of 20 ml.

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 of refrigerant 20 ml
Burst A/C hose 40 ml
Replacement of hose 20 ml
Replacement of condenser 40 ml
Replacement of evaporator 40 ml
Replacement of desiccant container 40 ml
Replacement of expansion valve 20 ml
Replacement of compressor* 70 ml*


*Note that the new compressor is filled with 200 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 200 ml of compressor oil.

If only the compressor is being changed, 130 ml of oil should be drained from the new compressor (200 - 70 = 130). If, for example, the desiccant container is also being changed, only 70 ml of oil should be drained from the compressor, as per the following example:

200 ml (in a new compressor)
-20 ml (lost during draining)
-40 ml (lost when changing the desiccant container)
-70 ml (lost when changing the compressor)
=70 ml (to be drained from the new compressor)