I just replaced a Copeland short head compressor with a new tall head compressor. Compressor had a failed valved which destroyed the top of the piston. During diagnostic, oil pressure was good at start up then dropped after compressor settled in tripping low oil pressure safety. I assume this indicated refrigerant in oil washing out oil causing oil pressure drop.
New compressor is installed and I am getting foaming in the oil sight glass. This is a 2 compressor Mammoth, water cooled condenser box car unit. This is the No. 2 compressor which is a 3 head with 2 electric unloaders. I have run all my test with compressor fully loaded (although light load on system) and No. 1 compressor off. DX coil for 2 circuits is mixed (not stacked).
Refrigerant pressures are approx 60/225 (depending on ambient). SH at DX outlet is about 20-21 degrees and 23-25 at compressor inlet. SC was 8-15 degrees (I have gauge on discharge and at liquid line filter drier and D/C was about 25 psig higher than LL so not sure what SC is for sure. Still need to verify gauge accuracy (was at the end of the day yesterday & had no time to verify that yet)).
I took apart the TXV and cleaned as best as possible since I had such dirty oil and looked like it may have been sticking. Still oil foam.
Crankcase heater is active when compressor is off.
Oil looks good for approx 30-45 seconds after start up then begins foaming.
Valved off suction service valve to 20 psig suction and still foams. If I open service valve approx. 1 turn open, foam clears for 3-5 seconds, then foams again. It will do this until service valve is open approx 25%, then no change with oil foam after that when valved opened in 1 turn incriments.
In comparison to other indentical unit (although slightly higher air volume and a couple of years older), same size compressors, same size TXV, and no foaming. Bottom of crankcase feels warmer on other unit compressor even when 2 heads unloaded, and No. 1 compressor for this unit. The new compressor crankcase temperature is considerably cooler, which makes me believe that I could still be getting refrigerant in the oil (just a thought). New compressor does have POE oil from factory and did not change. I heard that this oil is prone to foaming.
I have adjusted TXV and can get adjustment, with stem front seated, max SH was about 35 degrees, minimum was about 12 with stem open all the way. I have not yet removed bulb from suction line to see TXV response.
I was told by RSD Copeland guy briefly (he was on bereavment but answered phone anyway) and he was saying he thinks TXV is too big, although this is a factory installed item and neither the TXV or compressor has ever been replaced. He also said I should have 8-10 degrees at DX coil outlet (unless I misunderstood him) and 20+ SH at compressor. I am not sure how I am going to pick up 10+ degrees of SH on an insulated refrigerant line, inside a cabinet and not influenced by ambient temps or any type of hot gas bypass (the unit has one but only on No. 1 compressor). I still need to contact him again since that was a couple of weeks ago (I was on vacation last week) and hopefully he is thinking a little clearer now, so I am not relying on that information for now.