View Full Version : Would changing from mp39 to 134a

03-31-2016, 11:23 AM
Removing the mineral oil and replacing with POE oil and keeping a temp at 40 degrees give problems to the heat transfer? I found this article Retrofit Situations: Residual Mineral Oil in Polyol Ester
When retrofitting with an HFC it is necessary to flush as much mineral oil out of the system as possible
and refill with polyol ester. The amount of residual mineral oil left in the system can still have an impact on system
operation. Tests with pure 134a and POE with 5% mineral oil showed phase separation at 75"F for 20 wt% oil in
refrigerant, and the separation temperature was 39F for 2.8 wt% oil in refrigerant. When the amount of residual
mineral oil was reduced to 1% in POE, the separation temperature was 19 SF for 20 wt% oil in refrigerant.
The oil which separated from the mixture was almost all mineral oil, which means the majority of the oil
charge (95 to 99% POE) was still mixed with the liquid refrigerant. It is not likely that the system would suffer
from oil return problems in this situation. The mineral oil which separates, however, could still coat evaporator
tube surfaces and reduce heat transfer.