Copeland Discus Disc failures

[geno]

I have a customer with 5 Low Temperature Century Low Temperature Condensing units and respective 10 evaporators. Electric defrost 3 per day temperature terminated default time set to 40 min. Each 6DT3-300E-TSK handles 1 evaporator, 2 Compressors per unit. We are breaking up the valve plates (the disc is blowing out) causing oil washout etc. I know this is caused by Slugging of refrigerant or oil. But we check on the units weekly and are keeping the return gas between 25 and 30 degree superheat, subcooling is 12 -16 degrees. I have removed oil to 1/3 sight glass. I now have a suction pressure and temperature recorder on the latest failure. Any suggestions?

[GHAZ]

Hi geno are you using the right valve plates ,because there are 2 different types,one has stronger springs behind the poppet and the other slightly soft spring,are you using genuine copeland plates or remanufactured.When the springs get hot they might become flat and cause the discharge poppet to bounce around in the plate and break up.

[Mike NZ]

have you checked your compression ratio?

[geno]

I took apart the last failure and I've looked at alot of discus over the years and the spring seemed very soft. It's a remanufactured compressor and I'll bet it may have the wrong valve plate. Also my graphs are showing the compressor is leaking by during defrost to the tune of 4 times in 45 mins. Copland says 7 times in an hour is ok. Another problem is the sytem is still setup for low head operation 140# cutout for #1 condenser fan motor. 404A should be at 210#

[geno]

mike
I'll bet the low head is contributing to these failures. The latest info I found on these units has the head pressure settings at 200# and above. Thanks

[desA]

Do you think that the condenser fan is cutting out on too low a temp setting - so reducing condenser capacity, & ultimately raising suction pressure, hence discharge pressure/temp. So giving the disc a tough environment, leading to a softening of the spring?

[jasperreefers]

I know this is an old post but these compressor suction disc/reed damage is an old problem. you can catch them early before they do serious damage by checking the surface temp on the head above each piston, and they should all be about even at say 80c depending on operating conditions, if you get an odd temp thats a lot lower on one say 45 to 60c, it is a good indication of a cracked suction reed in the early stage

[rbsguzman]

I have a customer with 5 Low Temperature Century Low Temperature Condensing units and respective 10 evaporators. Electric defrost 3 per day temperature terminated default time set to 40 min. Each 6DT3-300E-TSK handles 1 evaporator, 2 Compressors per unit. We are breaking up the valve plates (the disc is blowing out) causing oil washout etc. I know this is caused by Slugging of refrigerant or oil. But we check on the units weekly and are keeping the return gas between 25 and 30 degree superheat, subcooling is 12 -16 degrees. I have removed oil to 1/3 sight glass. I now have a suction pressure and temperature recorder on the latest failure. Any suggestions?

First of all make yourself clear, Do you have 2 evaporator per unit or two compressors per unit?

[rbsguzman]

What kind of ambient temp this is running at, does it have crankcase heaters, how high above the evaporators are located,does it have pumpdown solenoid valves? make sure the TXV's are not affected by sub-cooling, it wiil tend to increase the mass flow rate in the evaporators causing floodbacks

[rbsguzman]

Also COPELAND likes 30 to 40F compressor superheat, especially on Discus