Dancing Copeland Semi-Hermetic

[rdmsqito]

Hey guys, has anyone ever seen this?
I have a 2HP Copeland semi-hermetic compressor that runs well and cools great. Problem is when the compressor shuts off pressure is going backwards through the compressor from high side to low side causing the unit to "dance" as it rotates in reverse. When the thermostat closes the solenoid the unit pumps down properly, the pressure control is shutting the compressor off at about 0 psi as it should, then the dancing starts. First thought was maybe electrical but cutting the power does nothing to stop it. It will either stop on its own after a minute or so or raise the low side pressure high enough that the pressure control starts the comp again until it pumps back down to 0 then starts all over. Closing the discharge valve while it's dancing will make it stop, so it's definately refrigerant passing back through. Thought maybe bad valves but compressor will pull 18inhg vacuum by itself. Any thoughts?

Unit is R408A, charge is good running 20 psi low/225 psi high. TIA
-Vinny

[taz24]

It will either stop on its own after a minute or so or raise the low side pressure high enough that the pressure control starts the comp again until it pumps back down to 0 then starts all over. Closing the discharge valve while it's dancing will make it stop, so it's definately refrigerant passing back through. Thought maybe bad valves but compressor will pull 18inhg vacuum by itself. Any thoughts?

Unit is R408A, charge is good running 20 psi low/225 psi high. TIA
-Vinny


I think you will find that it is one or more valves on the discharge that is faulty.
When the comp stops the high discharge pressure goes back to the suction and then the cycle starts all over.
You will need to strip the comp down and check the valve / valve plate.

Cheers taz.

[coolhibby1875]

this is a common fault with copelands the compressor is kaput and needs replaced

[PAXFREON]

Sounds like a bad valve plate or the internal reeds are allowing the pressuure to blled back thru.

Good luck bro

[US Iceman]

Thought maybe bad valves but Compressor (http://www.refrigeration-engineer.com/forums/glossary.php?do=viewglossary&term=60) will pull 18inhg vacuum by itself.


That only proves the suction valves are reasonably OK. You're problem is caused by the discharge valves. One or more are broken.

Pump down the compressor, de-energize the main & control power, close the discharge valves and suction valve (if you have not already done so). Recover the refrigerant out of the compressor and pull the head & valve plate off.

The next question to solve is; what broke the discharge valves in the first place?;)

[taz24]

this is a common fault with copelands the compressor is kaput and needs replaced

I disagree.
The comp may be repaired, as long as the damage is only the valve plate and valves.
If the pistons are shot then yes replace it but a top end service is fairly straight forward.

taz.

[markacs]

[quote=rdmsqito;77709]Hey guys, has anyone ever seen this?
I have a 2HP Copeland semi-hermetic compressor that runs well and cools great. Problem is when the compressor shuts off pressure is going backwards through the compressor from high side t

[rdmsqito]

Thanks all for the replies. When I opened the comp one of the valve reeds was installed backwards. Don't know who had it open the last time but nice job huh? Anyway, no more dancing!

[Abe]

Pax*****


"The early Bird get's the worm, But the second mouse get's the cheese"

Great sig mate, made me think a bit, and then it hit!!
:)