But when one quits working properly ... there are several reasons why this is happening.
One is a pluged screen.
Sometimes this occurs when an idiot replaces a compressor on a system which uses mineral oil and the new unit if filled with POE. This is something that happens in some of the markets I help take care of.
We are on 22 and the new units are all filled with POE. So we drain the oil and fill em back up with Mineral before installing them.
But whenever someone does NOT change that oil ... we have hell to pay.
Another reason a valve fails to function ios when some guy comes along and turns the adjustment screw until it meets the stop .... THEN KEEPS ON TURNING!
Then as Dave said in another thread, the valves fail to function when the power head loses it's charge. So the power head, in many cases, can be replaced and the valve returned to normal service.
Anyone have anything to add to this assortment of observations?