Oil solubility problems

[Pykester1]

Hi.
I am having an issue with oil solubility on a system that has been retrofitted from R.22 to R422d. The plant in question is a medium temperature DX air handling unit that evaporates at around -5 Celsius, and holds about 60kgs of refrigerant, with a 30 HP semi hermetic compressor. We have retrofitted to R422d on quite a few units of this type and have never had a problem, but on this particular system there is a large sight glass in the end of the receiver so it is possible to see the level of refrigerant in the receiver, and I have noticed that there is a thick layer of oil on top of the liquid refrigerant, which concerns me. Obviously the oil is not mixing with the refrigerant correctly, (I belive it is mineral oil) and although the unit has an oil separator and the oil level in the crankcase seems okay and the unit is not tripping out on the oil pressure switch, I am concerned for the future operation of the compressor. Does any one have any suggestions as to why this may be happening, and are there any ways to get the oil back to the crankcase?
Thanks in advance for any suggestions.

[Brian_UK]

We had a thread about this the other week and it seems that if you have a receiver then you should replace the mineral oil otherwise it settles at the top of the receiver.

http://www.refrigeration-engineer.com/forums/showthread.php?33924

[monkey spanners]

What Brian said!

Have a read here too,

http://www.certifiedrefrigerant.com/tecumsehguidelinesr22_hfc%20blends%20retrofit.pdf

I think a change to POE oil would be a good idea so long as the rest of the system is compatable.

I have been selecting POE lubricated compressors for replacement of failed mineral R22 one for this reason, though you have to be carefull as some manufacturers POE goes frothy with R22 (maneurop and possibly others)

Jon :)

[Fri3Oil System]

Hi,
that could be due to a phases separation. Oils get mixed between them, but MO does not mix with R422D, and that's why you lose lubricity and solubility with the refrigerant.

Regards,

Nando.