Running compressor 2 only gives me 56.7 to 61.2 pounds suction with 16.8-15.3 degrees of superheat. Running compressor 1 only gives me 57.6 to 61.2 pounds suction with 13.5-12.3 degrees superheat. The oil in the sight glass of the running compressor is only about 1/8 with foam filling the top 7/8 of the glass.
No not exactly, you need to shut the machine down, get the water nice and hot, turn it back on and run that circuit fully loaded, you may have to do this more than once, depending on your building load.
OK, going to try and flush oil out of the evaporator tube bundle. Turned off this chiller and the water flow through it this morning. The water in the barrel is now up around 70 degrees. Not sure how I can "get the water nice and hot", since the other chiller on the common primary loop will be down to temperature(46-48), when I turn this one back on. If I start this chiller and start putting 48 degree water through the tube bundle will I still have a chance of flushing the oil film back to the compressors?
This is a bit of a long shot but may be worth considering.
Is it possible that you have (some?) refrigerant by-passing the chiller and going directly into the suction line? I'm thinking you may have a damaged chiller head gasket. This would have the effect of driving down the superheat, closing off the expansion valve and causing the fluctuation that you see.
I've only seen that once in 40 years but it was on a new machine. (The gasket between the refrigerant inlet side and the suction side had separated during manufacture.) It's a bit more difficult to imagine it happening on an older machine.
Schafer, I suppose that is possible. Although the chiller is 10 years old, one of the two compressors on this circuit was replaced after about 2 years and I replaced the other one this past July. Since I just took over service on it back around the first of the year, I'm not sure of the problem history. What I do know is that it was overcharged by 20 pounds on a nameplate 65 pound charge. My assumption is this was the only way they could keep it from tripping out on LP.
As for the oil coating the evap tube theory, I did notice oil in the liquid line when I opened up the LSV to rebuild it. I'll try to flush the evap out by warming it up, but am not sure if the water side also needs to be warm for this to be effective. Thanks for your thoughts.
To properly put a load on that circuit, you need to shut the second machine down, isolating the barrel as you did accomplishes nothing, you also need to leave the pump on, to pick up the load from the building.
Eureka, I think the problem has been solved!!! I was able to leave this chiller off and let the barrel warm up overnight. After the church building went back into unoccupied for several hours, I was able to give the chiller a pretty good load with return water in the 60 degree range. As soon as both compressors on this circuit cycled on and ran for 2-3 minutes, oil came back to above the sight glass. I turned the chiller back off, recovered refrigerant out of the low side and drained about a gallon of oil between the two compressors, stopping at 1/2 glass on each compressor. I repeated the process a second time until oil filled the sight glasses and drained another gallon of oil. Suction pressure is now steady at about 62# and oil levels in compressors appear normal. These two gallons of oil must have been coating the evaporator tubes as well as the inside surfaces of the condenser and liquid line. Thank you everyone for helping me stretch my mind!