Copeland Scroll shutting down

[Arkma]

I have a Copeland Scroll #ZB11MA-TWD-551 that keeps shutting down on the motor protection module. it shuts down about 3 sec after it starts. We at one time thought we had it nailed down to a voltage imbalance, however the last time it shut down the voltage was pretty equal across all three legs. At least it was within the 3% that Copeland recommends. Anyone know how common it is for these modules to go bad? The module is a Kriwan 071-0547-00. This system will work sometimes and sometimes it won't. It seems once it runns past a 1/2 hr or so the customer is fine until he shuts it down on the weekend.

By the way this compressor is being used on a 15 ton water cooled portable chiller, making chilled water at 50 F. System parameters when running 18F sh, 12F sc, 280 hp, 50 lp.

Any advice on what to do next?

[chemi-cool]

hi arkma,

i would suggest first to disconnect the compressor from the system and let it run for a minute with no resistance.

if the guts are ok then the problem could be an obstruction in the discharge.

compare the the head pressure with another compressor.

scrolls are very sensitive to high pressure=heat.

please let us know what you have found.

chemi

[chemi-cool]

I have found for you some more information, have not read it yet, I hope it will shed some more light.

http://www.copeland-corp.com/americas/ae1302.pdf

chemi

[Arkma]

Chemi,
Thanks for all the info...at this point I don't have the luxuary of having the customer disconnect the compressor. I'll keep you posted..anything else you can think of would be helpful.

Arkma

[Gary]

Telling us the pressures doesn't do much good if we don't know what refrigerant is being used.

[Arkma]

Sorry...R-22

[Gary]

The high side pressure seems excessive. Is the condenser clean? Is the fan running in the right direction? At what points are you measuring subcooling and superheat? Is the compressor above or below the evaporator?

[Gary]

Is this a TXV system? Does it have an EPR or other capacity control device? How is the water temperature being regulated? How exactly is the subcooling and superheat being calculated?

[Arkma]

Unit is water cooled. Compressor is below the evap by about 1 foot. Subcooling at the outlet of the reciever, superheat at the TX bulb.

[Gary]

Unit is water cooled. Compressor is below the evap by about 1 foot. Subcooling at the outlet of the reciever, superheat at the TX bulb.

Is the condenser using tower water or domestic water? What are the condenser entering and leaving water temps?

[Gary]

Whenever the compressor is below the evaporator there is a potential problem on startup.

During the off cycle, liquid refrigerant will accumulate in the coldest part of the system, which is usually the evaporator. If the suction line loops above the evaporator before going down to the compressor, then that liquid is contained in the evaporator. However, if the suction line goes straight down to the compressor, then gravity will deliver that liquid to the compressor, and the compressor can be full of liquid on startup.

Options are to loop the suction line above the evap and/or to close a liquid line solenoid on shutdown with or without pumpdown, so that refrigerant cannot travel to the evap. Another option would be to install an accumulator to catch the liquid.

Compounding this, if the system has been overcharged, there is more refrigerant to gather in the evap.

I am looking for clues here, and that high side pressure jumps right off the page at me.

[Peter_1]

Arkma,
It should be polite if you told us what was wrong with the unit.

[Arkma]

Arkma,
It should be polite if you told us what was wrong with the unit.

We rplaced the module and the unit has been running fine ever since. Sorry I didn't get back to you guys, your always so helpful. Not very thoughtful on my behalf.