Scroll Compressor Seizure

[jwasir]

Hi,

I designed a refrigeration systems for a falling film chiller.

It is supposed to maintain 35F water temp for salad processing unit.

Both the systems has similar conditions.

One system is equipped with Bitzer Semi Herm. compressor and is running fine from last ONE year.

Second System has Copeland Scroll compressor, which has been replaced for FOUR times in last ONE year.

Last compressor only ran for 1 month and got seized.

Everytime after the compressor replacement, both the suction and liquid filters are replaced with the oil.

Last time, some acid was found in the system, which has been cleaned by changing the oil 4-5 times.

After changing last comp., oil acid test is found GOOD.

Copeland report says that failure happened due to refrigerant dilution.

System superheat is 18F, subcooling, discharge temp, etc all is within envelop.

Comp is appox 10' higher than falling film evap.

It has continous pump-down cycle and HG by-pass.

Indoor application, room maintained at 70-75F.

Comp. has Crank case heater, which was found to be defective in last compressor.

Can you suggest, what could be the reason????????

Can too much oil cause refrigerant dilution??

Any other paramets, which can be checked/adjusted?

Oil return in the system seems not to be problem.

Evap outlet has U bend for oil return!!

[nike123]

?

Can too much oil cause refrigerant dilution??



No! But liquid refrigerant in crankcase could cause oil dilution. That is the cause of last Copeland compressor seizure by Copeland report.
Also, you found that at last compressor crankcase heater is defective. That has caused compressor seizure, because measures as pump-down, obviously don't work satisfactory.
What are conditions around compressors regarding possibility that compressor is coldest place in instalation?
What was previous compressors cause for death?
Do you have refrigerant diagram to show!

Check this Copeland buletin:
http://www.hvacrinfo.com/cope_ae_bulletins/TAE1182.PDF

[monkey spanners]

Hi Jwasir,

How frequently does the compressor stop and start?
I have found that copeland scrolls seem to pump out some oil on starting, too frequent starting seems to lower the oil level quicker than it returns to the compressor, this was on milk tank dx systems.

Jon

[US Iceman]

If the problem was reported as oil dilution then the compressor is most likely experiencing flooded starts or low suction superheat.

If the oil heater had failed that might be part of the total problem, but if compressors are failing every three months or so then I would concentrate on what might be causing the the liquid accumulation in the compressor.

[jwasir]

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Compressor is located above the Falling Film Chiller and ambient temp is around 70-72F.

Copelend report for previous comp is still pending.

Comp. runs for approx. 30-40 mins and stops for 10-15 mins.

We have continous pump down, how can we check and avoid flooded starts?????? Superheat seems to be ok.

[US Iceman]

Comp. runs for approx. 30-40 mins and stops for 10-15 mins.


Why doesn't the hot gas bypass cause the system to run longer?




Superheat seems to be ok.


It either is, or it's not. Are you sure? 30-40 minutes is not enough time to adjust a TXV and gain stable operation. If you are trying to set the TXV when the run cycle is short the valve may be hunting when you are not watching it.

This is probably my best guess right now based on the comments so far.

[jwasir]

I Can Double Check The Time With Hg.

How Can I Check/avoid Flooded Starts?

[jwasir]

Hi All,

After adjusting the HG by-pass, system runs for approx 2 hours and stops for 1/2 hr.

Again, the super heat seems to be fine 18F.

I would like to know what should be the right pressure for Pump Down?

Should the system be taken to 0 PSIG or some higher pressure?

Thanks in advance!

[nike123]

How Can I Check/avoid Flooded Starts?

I think that answer is in Copeland bulletin which I posted earlier!

[icecube51]

try to mount and inverter regulater system, so the comp. dont have to frequently stop and restart,but stays on a regular working base.


is it the correct type,ho has made power calculations??

Ice