oil pressure

[claude11]

I was doing some work on a semi - hermetic copeland compresor. The suction and discharge were both at atmospheric (0 psi) . I had it pumped down for the winter . when I removed the plug to do an oil change , oil blew out , I guess the pressure in the base was at 15 - 20 psi . This compressor had gone out on oil pressure several times during the past season . shouldn't the base pressure have been the same as the suction ,0 psi ???
What could cause the base pressure to be higher than the suction and discharge prussure ???

[old gas bottle]

you had pressure traped in the crankcase as you found out by having a oil shower if its the larger body machine with the suction valve on the end it may have a check valve between the motor case and the compressor case to stop leakage back up the suction so it could in theory have gas in the crankcase without showing on the gauge, it would not happen if you just pumped it down and then worked on it but if left pumped down some leakage could filter through into the crankcase but not back to the suction port.

something you only find out when you see one cut open if its the one with the valves on the side of the head it may have just been liquid sat in the oil.

[chemi-cool]

Have you checked the oil filter? Or the the oil pump?


Chemi

[monkey spanners]

When i used to do a lot of oil changes for cfc to hfc conversions i soon learned in the winter to run the compressor until the sump was warm.I could run the compressor for a few minute, pump down to 0psi shut the valves, remove the sump plug without a problem until i fed the pipe into the sump to suck out the oil, this would disturb the oil and result in a fountain out the plug hole despite the compressor being at 0psi. The weight of the oil stops the refrigerant from boiling until disturbed. Soon learn to run them for 20 or 30 minutes.

Jon

[powell]

claude11,

Since it has a lube oil control this would be a refrigerant cooled compressor. You also stated problems with the LOC tripping in the past. Here's a couple of quick thoughts I have.

1. The crank was pressurized causing the check valve to close (2 psi diff or more) between the crank and motor compartment. The motor compartment has the same pressure reading as the suction service valve. This condition is caused by worn cylinder walls due to overheating which causes LOC trips.

2. There could have been liquid refrigerant trapped under the oil due to excessive floodback conditions when it was operating, causing the LOC trips. Maybe this liquid boiled off after you pumped it down and it set idle.

If you disire to discuss this in more detail, give us the model number of the Copeland compressor. Some compressors have an internal crankcase ventilation valve that might come into play.

[powell]

Here's an internal view of a typical refrigerant cooled Copeland compressor. Just in case anyone wants to see it.

[claude11]

Thanks to all
The compressor model is 6DL1-2700-TSE
I'm thinking it was the check valve ( now that I know it's there) .I guess you could test the pressure on the Schrader valve near the pump ( where you put oil in ) to check if there is any pressure ?