Do you need to remove the old compressor oil when converting 134A from R12 Freon and refill with new compatible with134A?

Yes, it is generally recommended to remove (purge) the old compressor oil and replace it with new PAG oil when converting an air conditioning system from R12 Freon to R134A refrigerant.

Here are a few reasons why it's important to change the compressor oil:

- Miscibility: PAG oil is hygroscopic, meaning it absorbs moisture from the air. When mixed with mineral oil, which is commonly used in R12 systems, the two oils can form a mixture that is less effective at lubricating the compressor and can lead to premature wear and failure.

- Viscosity: PAG oil has a lower viscosity than mineral oil. This means that it flows more easily and provides better lubrication at lower temperatures, which can improve the efficiency of the air conditioning system.

- Compatibility: R134A refrigerant is not compatible with mineral oil, and using the wrong type of oil can damage the compressor and other system components. PAG oil is specifically designed for use with R134A and is compatible with the materials used in the air conditioning system.

To ensure proper conversion and long-term performance of the air conditioning system, it is best to follow the manufacturer's recommendations and use compatible components, including compressor oil, refrigerant, and any necessary seals or gaskets.