I have a customer with a York chiller with two of a York Model PA842-V46/50CN reciprocating compressors. The system 1 compressor shut down on low oil pressure last night. I reset it today and had 80+ psi net oil pressure and the compressor ran for 1 hour and 20 minutes before the oil pressure began to drop. It is a process chiller set to maintain 40 degrees. The system 1 compressor was the only one running while I was watching it, the water temp was 42 degrees, suction 45psi, discharge 205psi, sump temp 111 with a superheat at the compressor of 21 degrees and the oil level is between the upper and lower glasses. The oil pressure dropped slowly over the next 15 minutes until it locked out at 25 psi. I also noticed that from when the oil pressure first started to drop until it locked out the pressure was pulsating so that my gauge fluttered about 10 psi or so. Before that it was rock steady.
I let the compressor sit for about 15 minutes and restarted it and the oil pressure was up to 70 psi net but still fluttering and within 5 minutes or so it shut down again. Drew off an oil sample and it looks like new.
Any ideas why the oil pressure is dropping?