Copeland Semi-Hermetic Compressor, Rae Corp/Century Refrigeration

[Fett]

Good Afternoon Gents,

I have a century refrigeration "D" series unit. It has in parallel, two 20hp Copeland Semi-Hermetic compressors. This is an R-22 system, high temperature. Room temperature is set at 76 F. Outdoor ambient temp is anywhere between 90F-115F. This unit only operates during May-Aug. It is 7 years old. Has its own separate oil resevoir, each compressor has its own oil regulator and there is an oil seperator/solenoid valve downstream of the compressors.

The problem I am having is my second stage compressor, the lube oil safety switch is dropping out after roughly 20-30 minutes of compressor operation. I have replaced the lube oil safety. Removed the oil pickup screen from the compressor and to clean it out but it was clear with no debri in it. Still drops out. With my guage on the oil port it reads, flutters between 60-80psi while the compressor is operating. When I put the guage on 1st stage compressor it does not flutter at all and is right at 60psi.

The only other work I have done to this unit other than pre and post operation checks and mid-season inspection is cleaning of the condensor and evaporator coils and replacement of the bearings in the condensor fan motors(x4 fans). This is a 460volt 60hz 3phase system, my average incoming voltage is 485-490v so my actual amperage while operating is slightly lower than rated amperage.

I am an in house tech and I don't have alot of experience with large units. We have two of these units here. Any assistance is helpful thanks!

[Magoo]

Hi Fett.
the fluttering could indicate the oil relief valve is on the blink. It is accessible on back bearing housing.

[Fett]

Ok, I have ordered an oil pump kit from A-1 compressors. In the mean time. I started this unit yesterday afternoon. We have had a very cool year thus far so have not needed to operate the unit up to this point.

To start, room temp 81F
ambient temp 91.8F
set temp, 70

Panels come off the unit, check oil sight glasses, both are at 3/4 level. Crankcases are warm to the touch(power has been applied to the unit for 7 days)
Flip the switch from off to on, the liquid line solenoids open, can hear the refrigerant flow. 10 seconds later stage one compressor kicks on @ 180psi, the unloader loads at 200
stage two compressor kicks on @ 220, unloader loads at 250,
initial system pressure with high heat load, 278psi
low side is at 80psi
both sight glasses pre and post subcooler loop showing flash gas
both compressors are running at 28.2-28.9 amps between L1,L2,L3, RLA is 33.3 amps.
Two hours goes by, I check system again.
System pressure
high side 263
low side 75
Both compressors are still running, loaded still right at 28.2-28.9 amps
compressor 1 sight glass is at 1/3rd level with 1/4" of foam visible ontop of oil.
compressor 2 sight glass is at 1/2 level with no foam visible ontop of oil
refrigerant sight glass pre subcooler loop shows slight flash gas
post subcooler loop shows no flash gas, both have solid green dot.
ambient temp is 92, condenser outlet air temp is 115. room temp is 77. (the room is about 150,000sq ft with 36ft high ceiling)

Is there anything else that I need to be checking?

[Rob White]

.

You need to measure the difference between the oil pump pressure
and the crank case pressure, that is the pressure difference that
the oil differential switch measures.

The switch is adjustable but it will required a difference between the
pump pressure and the crank pressure to run.

Different machines have different pressures but at least 1 to 2 bar (15 to 30 psi)
would be the norm so see what the difference is.

If the comp is getting a bit slack due to wear inside then the difference between
the pump and crank pressure will drop, if it drops bellow set point on the switch
for between 90 and 180 seconds then it will trip out.

Regards

Rob

.

[Martin Davies]

In the two hour period, did the room reach temp and shut them down? Or did they continually run? Also is there only 1 oil separator or 1 for each comp? A picture of the setup would be really good if possible

[Glenn Moore]

Hi Fett
Your system seems to be well short of charge, if your sub cooler is not showing a clear sight glass. With the low side guage reading 75 psi which equates to evaporating at approx. 43deg F with air on the evaporator at 77degF which gives an approach condition of 34 deg, which is much to high. This could cause the compressors to run with an extremely high suction superheat, with a corresponding high discharge superheat which may be causing the compressor oil to run extremely hot and reducing its viscosity, to appoint that it cannot be pumped correctly . You need to get the refrigerant charge checked and topped up (if still legal) and then check the expansion valve settings to make sure that the system is working efficiently. With the plant running you need to measure the suction pressure and also the suction pipe temperature ,if possible close to the expansion valves thermal bulb . lets have some more readings and we can advise further.

[Fett]

Hey gents, thank you for help, issue not resolved yet (so much stuff to do around here). I will have more readings tomorrow or wed.

[Fett]

In the two hour period, did the room reach temp and shut them down? Or did they continually run? Also is there only 1 oil separator or 1 for each comp? A picture of the setup would be really good if possible

System is Parallel, Large suction line filter then two suction line accumulators(one for each comp), then suction line into compressors, compressors both discharge into one large oil separator, bottom of separator is a solenoid with 3/8th" OD tubing running back to the oil resevoir, after the oil separator the refrigerant plumbing goes into the liquid line receiver tank, then to the condensor, comes out of the condensor and goes through a filter, then through the subcooler loop and one last liquid line filter before going to the evaporators. The liquid line comes from the condensing unit. It "Ts" into two directions, each side with a liquid line solenoid. One L.Line Solenoid goes to 3 evaporators (controlled by thermostat #1) and the other L.Line Solenoid goes to 2 evaporators(controlled by thermostat #2). Total of 5 Evaporators, compressor operation is controlled solely by pressure switches as are condensor fan motor operation.

Thermostat # 1 is set for 70F and Thermostat # 2 is set for 72F.

The system went from 81F to 77F in the two hours that I was able to observe the system. So no it did not reach room temp within two hours. Granted this space is excessively large with alot of energy to move.

[Fett]

Hi Fett
Your system seems to be well short of charge, if your sub cooler is not showing a clear sight glass. With the low side guage reading 75 psi which equates to evaporating at approx. 43deg F with air on the evaporator at 77degF which gives an approach condition of 34 deg, which is much to high. This could cause the compressors to run with an extremely high suction superheat, with a corresponding high discharge superheat which may be causing the compressor oil to run extremely hot and reducing its viscosity, to appoint that it cannot be pumped correctly . You need to get the refrigerant charge checked and topped up (if still legal) and then check the expansion valve settings to make sure that the system is working efficiently. With the plant running you need to measure the suction pressure and also the suction pipe temperature ,if possible close to the expansion valves thermal bulb . lets have some more readings and we can advise further.

I have two liquid line sight glasses, one before the subcooling loop and one after. When I first started the system up, both sigh glasses were heavy with flash gas. I assume this is because of a high heat load and that the system had not balanced out.

After I checked again two hours later the sight glass before the subcooling loop had minor flash gas and the window after the subcooling loop was solid refrigerant.

Both dots are green.

[Fett]

Hi Fett.
the fluttering could indicate the oil relief valve is on the blink. It is accessible on back bearing housing.

Hey Magoo, the breakdown of the oil pump assembly shows that the oil relief valve is spring loaded and non-adjustable and says do not disassemble.

[nike123]

after the oil separator the refrigerant plumbing goes into the liquid line receiver tank, then to the condensor, comes out of the condensor and goes through a filter,

Iether your description here is not correct, or system is not assembled correctly.
Liquid receiver cannot be before condenser, since there is no liquid before condensation!

Is this your oil level regulation system?

Screenshot from 2015-06-04 13:13:36.png

[Fett]

Nike123, you are correct, the liquid reciever is after the condenser but before the subcooling loop. Yes that diagram appears to be the correct oil control system that I have. On my compressors are the Sporlan Oil Level Control, Type: OL-60NH-2. The refrigerant/oil separator is a Henry S-1903 precharged with 20oz oil.

I am going to check for an oil strainer downstream of the oil resevoir. I don't recall seeing one.

[nike123]

As stated earlier, you should check total superheat at compressor entrance ( on pipe 20 cm from compressor valve) Maybe, when heat load became lower as cold-room approaches set temperature, total superheat will be low enough to not affect oil viscosity!

[Martin Davies]

I have a similar problem to this but sadly do not have the answer for you. I have 3 comps linked to 1 oil reservoir each with their own separators. The furthest away from the reservoir is the first stage comp and is run by inverter. The other two never have low oil faults but comp #1 will run on and off for a few days and then randomly trips out on low oil. There is more than enough oil in the reservoir to supply all of the comps but it still trips, usually out of hours so I can't be there to see it happen.

[Glenn Moore]

Hi Martin
This problem could be caused by the difference in crankcase pressure from the invertor machine to the fixed speed machines. The vent valve on top of the reservoir has a pressure spring to keep the reservoir pressure approx. 1.5 Bar above the crankcase pressure , but some of these vent valves have a lower value spring 0.2 Bar, 0.5 Bar etc, The spring value is normally stamped on the base of the vent valve. If the value is too low, this may cause the invertor machines crankcase pressure to be to high preventing oil to flow into the machine. Try fitting an ESK float as you can set them for up to 3/4 of a sight glass, I have experienced compressors tripping on oil failure due to the oil float not calling for oil due to the adaptor tube causing a weir effect between the compressor oil level and the oil float level, ie the compressor oil level is low but the float level is good . Fitting a 3/4 level float removes the weir effect of the adaptor tube. Also make sure the vent valve is a 1.5 Bar version.

[Fett]

Getting my butt kicked over here. 110-115F for the rest of the week and half of next week. Nothing but call after call after call.

[Martin Davies]

Thanks Glenn I will look into this today.

Fett can you post a picture of the set up?

[D.D.KORANNE]

Since the oil safety switch cuts off the compressor , probably you may have liquid coming in the compressor crank case . Liquid-oil mix cannot generate enough oil pressure to hold the switch in cut-in position .

I suggest to verify my point & try resolve the liquid slop-over issue .

Rgds ,
d d koranne

[Martin Davies]

Hi Glenn I've seen what I think is the vent valve that you mentioned and it is stamped with 1.4 bar - 20 psi so I'm assuming this is ok for an inverter driven bitzer. 1 of the stores that is cooled by this compressor pack has had its temperature increased from 4 to 13 degrees for storing a different product and since this change the comp hasn't tripped out at all! I haven't changed anything else so must be linked to previous issues

[RANGER1]

Fett,
What is set up for the liquid subcooling?
Maybe it's flooding that 1 compressor.
Monitoring discharge temp is one way of determining liquid carry over, as if not from evaporators, oil level foaming in 1 compressor, assuming oil pressure is ok ie total oil pressure minus suction pressure.