Compressor Cycling

[nlester]

I currently have a discuss type compressor w/ a low/diff switch. The switch is set to cut in a 25 cut out at 10. The switch is tubed to the compressors low side, not in suction or discharge lines. The problem I am having is that the suction pressure out on the unit is reading 53 psig, but the low switch is cutting the compressor off, causing the compressor to cycle rapidly. I then hooked a pressure gage between the switch and the compressor and the pressure reading was much less than the suction line. I do have a hot gas bypass but I have blocked it off at this point as to not put any additional pressure on the suction line.

What could be the possible reason that would cause this pressure differential between the low side of the compressor and suction lines?

Any suggestions would be helpful.

[monkey spanners]

Some of the smaller copeland/prestcold compressor have a wire gauze strainer between the suction valve and the suction port in the compressor body, maybe this is partialy restricted if it has one. once found a piece of building block in one, system had run for 20+ years until it wore through the strainer and smashed all the valves. Is it a replacement compressor, i've seen plastic plugs left in ports before.
If you turn the compressor off does the pressure to the LP switch rise to match that of the suction? if so look for a restricion between the two points you are taking you pressure measurements from.
What oil and refrigerant is it running on?

Jon

[nlester]

After I left my thread, I removed the suction valve screen and it was full of depris. I dont think the lines were cleaned properly before installation. Most of the material was not magnetic. Seems to have fixed the problem.