Using white mineral oil as compressor lubricant

[The Kelvinator]

I have constructed an air source heat pump for heating a hot tub and was wondering if using pharmaceutical grade white mineral oil is a good idea. I am using the white mineral oil in it just now and it has had about 24 hours of use on this oil without problems. Compressor gets warm but never too hot. The compressor is a 3/4 hp Danfoss SC21F and I am using HC12a refrigerant which is a mix of R290 and R600a. The original polyolester oil was completely flushed out and replaced with the mineral.

[Brian_UK]

Is the oil suitable for the expected temperature range of the system?

Do the manufacturers recommend its use with refrigerants?

Or, more simply, why not use the correct refrigerant oil?

[The Kelvinator]

I can't use the correct oil as I can't find anywhere to buy it. With the discharge operating at 60 to 70 degrees C it should be fine temperature wise.

[monkey spanners]

Suniso 3GS should be available from any fridge wholesalers, though they may need to order it in as not common now.

[chemi-cool]

Only refrigerant oil can be used!!
Refrigerant oils have the wax removed so they don't crystallized at low evaporating temp.
Pharmaceutical grade white mineral oil can be used like it says, pharmaceutical uses.

[The Kelvinator]

It's been fine so far, the evaporator works at close to freezing but is usually a few degrees above. I once used it in a system where the evaporator was so cold that my fingers stuck to it instantly and even then it still worked. I'm mainly concerned with it breaking down over time.

[Magoo]

Fairly sure the oil industry people call white oil, BASE stock oil before they dehydrate it, remove waxes and add anti foaming agents.

[The Kelvinator]

I got lucky and found 20 litres of Suniso 3gs on ebay for £32. I will just have to sell the extra!