Testing the Compressor:
If for any reason the compressor is not pumping sufficient gas, it is obvious that poor performance is the result. This can
be caused by leaky valves. To ascertain whether the valves are leaking, use the following method;
A compound gauge is installed at the suction service valve. Shut off the suction line after having started the compressor.
A hammering sound, coming from the cylinder head, indicates that an excessive amount of oil is being pumped through
the compressor. Oil is incompressible and its presence in the cylinder and passing through the valves is the cause of the
hammering. The valves are designed to stand this abuse. It nevertheless is undesirable because the oil is gradually
being transferred to the condenser and receiver, which means that insufficient oil remains in the crankcase to lubricate the
compressor. As soon as the compressor starts to pump oil, the motor should be shut-off for a short period of time, and
then restarted and stopped until quiet operation of the compressor is secured.
All during this time, the compound gauge should be given careful attention and when the compressor pumps a 24" to 26"
vacuum or more, it is functioning properly. If and when a 24" to 26" vacuum is attained, the motor should be shut off, and
the compound gauge carefully watched. In event the loss of vacuum is pronounced, that is, the back pressure readings
advance to a pressure within a short period of time, kt is a very good indication of a leaky discharge valve.