I started this as a new thread so this procedure wouldn't get lost in lynn rodenmayer's post of 7/14/04. I think it is important to understand. On a Copeland refrigerant cooled compressor the following can be used to determine piston blow by.
The oil check valve is NOT spring loaded. It is either a free floating ball or flat disc operated by the direction of oil flow. Any higher pressure in the crankcase is bad news, the ½ pound would be correct, and yes a ½ pound would be difficult to see.
To check; put a gauge on the crankcase and another on the suction service valve. Let's say they both read 20psi. Start closing the SUCTION service valve. When the pressures begin to drop (pumping down), now close the suction slowing and watch both gauges. They should pull down together, all the way down, how ever far it will go.
Let's say at 5psi the crankcase doesn't drop any more and the suction pulls lower. That is the point (5psi) where the crankcase pressure is overcoming the internal VENT valve and the oil check valve will now close. The check valve closes because of the reverse flow of oil direction.
[Edited by basser on 08-09-2004 at 08:43 AM]