Intermitent oil failure problem

[ironmen]

Hi guys

Today has been a very bad day.
I am working on a medium temp refrigeration system, running on R408 and it has been tripping on oil safety about 8 to 10 times in the past 3 months. There has been previous technician working on that system and no one has been able to figure out whats causing the fault, and today i have been sent on the job to find out what's wrong. I have check the oil pressure and found it ok.
Just to give you an idea as to what i have seen; it's an old rack system with 2 compressors serving a couple of walking cold room and display cases and i don't even know what brand it is. One compressor has just been replaced, which is a Copeland compressor model D4SAI-200X-AWM/D, altogether its got only 2 compressors and a lot of modification has been done such as cancellation of pipe work etc.
Today i have taken the following readings;
suction pressure 45PSI
discharge pressure 200PSI
Oil pessure 85PSI
Discharge Temp 80 degrees celcius
suction temp -8 degrees celcius
liquid temp -26 degrees celcius
ambient temp 18 degrees celcius

Hope i could get some help with this one.

Cheers

[sedgy]

hi ironmen, have you tested the oil pressure switch?,
remove the fuses for the comp, switch on < the comp should not run< time the oil trip swich should be aprox 90 seconds , the switch will take a few mins to cool down< there is a heater init< so from there you can see if its the oil switch or a problem in the comp, all the best

[ironmen]

Hi sedgy some more details its better thks.

[lowcool]

sedgy just described how to test/check oil failure control,if filter is clear check for faceplate wear in oil pump if thats ok you may have crap holding a solenoid valve open and or liquid coming back.wouldnt hurt to raise your head pressure

[ironmen]

Ive test the oil switch the other day by disconecting the compressor on the contactor thermal overload and turn back on and after the time delay approx 120 second it trip.but the funny thing is today ive seen it trip but the oil pump pressure was 70psi and the crankcase was 20,there is no oilpressure drop when it trip. 50 psi oil pressure more than enough.which is comfusing.its a new copeland comp and the unit repeating going on cycle evry 2 minutes on- off.

[sedgy]

hi ironman
yes the oil pressure swich can be set between 90 and 120 seconds, 50 psi is ample, the oil p,s,dose not just trip if the psi drops, it puts a heater ON if the psi drops for more than the set time, by then the heater has tripped out the oil p,s, I would still go with the oil p,s, but as do as LOWCOOL says letter 4 above, all the best ironman.

[coolhibby1875]

your nrv on the discharge will be faulty, i,e stuck open and when comp is not running the discharge presure comes back and washes oil away, then when comp starts it trips on oil.

[fowlie]

faulty oil switch

[IMSTIEN]

Check the run capacitor ,compressor may be cutting off from the overload protector,therefore trips the oil pressure safety switch.

[IMSTIEN]

If it is a 3 phase then check for loose connection /voltage imbalance.

[dirk]

If it is only the one compressor tripping swop oil pressure switches on compressors if the other compressor now trips the switch is probably faulty, if the same compressor trips you have a system fault.On rack systems with multiple cases, rooms intermittent faults like this can become a nightmare as you have so many variables. The best approach is to one by one eliminate all the possible causes either by installing monitoring equipment changing settings or changing over parts.
It may just be as simple as changing defrost scheduling.condensing or compressor cycling.
I can recall a similar problem that took 3 months to solve eventually it was found that at times one of the merchandisers was switching off the case fans when packing as he did not like the cold air blowing onto him.

[ironmen]

Hi guys here we go,this morning when i got to the plant room red light.its gone again and thanks to the back up compressor kick in and keeping the customer happy.I was talking to one of the mechanic this morning and he said to me that evry winter that system trip and he said to me that both compressor trip but not at the same time.Each compressor have its own oil pressure switch so its not the switch.But today ive removed the compressor contactor and open it and found alot of carbon inside i was getting a .2 volts drop on the blue phase.Ive replaced it by a new one and also increase my head pressure a bit.weather condition 5 degrees celcuis in the morning and stay around 20 all day after 11am.so anyway will see what happen if any one out there have come across this kind of problem pls share your experience.Just to let you khow guys my NRV on the discharge is good and my condenser is located on the roof,pipe work 3 metres from comp vertical to the condenser.thanks to you all i will keep you inform.

[australian tech]

G'day ironmen,I reckon Dirks on the right track. What sort of defrost cycle does it have, is it possible your getting a bit of liquid back on start up. tx or solonoid may be leaking thru, oil pressure can drop with the presence of liquid in the sump.
Does it have a high side float on the oil return . if it has an oil sep. there may be crap blocking the needle and seat. although chances are you would have noticed oil level fluctuation.

[ironmen]

Hi Aussie Tech, I ve seen this thing tripping on a 40 psi oil pressure,its got an interval defrost twice a day.Its got an oil separator on it,just assume that if there was a leaking tx but what about the reciever all the liquid will migrate in it.correct me.

[ironmen]

Sorry a leaking solenoid.

[sedgy]

hey ironman, glad you got to the bottom of the problem, and thanks for giving us all the outcome, cos now we all know, < a lot of engineers dont come back with the answer to the problem ,

[australian tech]

hey ironman, glad you got to the bottom of the problem, and thanks for giving us all the outcome, cos now we all know, < a lot of engineers dont come back with the answer to the problem ,


Sorry a leaking solenoid.
sorry ironman,
are you saying it is the solonoid leaking, or were you editing your last post.
:)

[ironmen]

No sedgy i havent get over this problem yet,in my last post i was just correcting the line that say tx and replacing it by solenoid.a little mistake in my part.but what i was saying is when you got a solenoid leaking, liquid will remigrate in your reciever right.

[australian tech]

If your sure it (oil press. swtch) is tripping when there is sufficient oil pressure ..(you say 40 psi.)
Is the switch getting the right pressure .ie the guage port and
o/p switch are getting good pressure sensing,what sort of pressure switch is it bro,is it danfoss mp55 capillary, is there isolation valves on the measure points .

Just to clarify, if the liquid solonoid was leaking (during defrost). the liquid (refrigerant) would migrate to the evaporator. Then on start up, (after defrost) cold liquid can come back ,filling the accumulator and the compressor sump,causing oil pump to pump gas rather than good thick oil.
That said.. you would notice the frost on suction line/ comp.sight glass.
Can you give us more details about system, type of oil return system
, do both compressors share common oil line (balance line).
is there a door switch operating liquid solonoid?
As always, the more specs, you can give,The easier it is to avoid dudes like me rambling on about stuff you already know.


ahh...all knowledge is good.Its what we do with it that matters.

[ironmen]

Hi aussie tech,on that system there is 4 solenoid valve that comes out from the liquid reciever in parallel.3 of the solenoid valve operate 3 walkin cool room and the last one operate on two walkin and a large display cases.But all three of them got there own solenoid upstream.but what ive notice the suction line that control the 2 walkin and the display cases frosted some time not all the time.there is a possibility maybe there is a valve leaking on those one because its got 3 on that line.and their solenoid next to the reciever stay open all the time.It is a danfoss mp55 and there is no isolation valve at the measure point.Its got a oil separator that share both compressor and a common line and runing on Ester oil.It was working on 502 before and the person who did the retrofit did not relpace the txv its still on 502 valve.anyway bye for now.

[lowcool]

i always replace oil failure when fitting new comp.has this one been replaced during previous failures.i should be up their for the v8s are you in darwin?or alice going by the ambient temp?

[oldesky]

Sometimes when you have intermittent oil faults on old systems it is caused by worn TX valves. I would suggest you change TX valves and reset superheats. You could change one at a time to see if a particular valve is causing your problem if you have the time and the client has the patience.

[Pykester1]

I think Oldeski might be on the right track. I have just recently had the same intermittent oil tripping problem on a crop cooling unit with a Carlyle compressor. I replaced the oil pressure switch but to no avail. In the end I found a faulty Danfoss TQ type electroninc expansion valve was the cause of the problem. Every now and then it was operating erratically and flooding the sump with liquid and diluting the oil. Check the superheats on each individual system.
Hope this helps.

[ironmen]

HI all,thks to reply so far ive discovered 2 solenoid not holding and ive seen 2 txv not operating properly ive just isolate the two txv for the moment and replaced the 2 solenoid and my system superheat is much better.but i thought ive found the problem:) But this thing trip again:mad: ive replaced a new switch and see how it goes.

[ironmen]

Hi guys this thing trip again.

[lowcool]

if you have been monitoring it and all is ok make sure the control is the last part of the control circuit.

[NoNickName]

How is it the suction is -8°C and the liquid is -26°C?

[ironmen]

Mr nonicname ive done a mistake in typing 26 degrees liquid line.

[Below 0]

you say its an old rack.there isnt a common oil line between the two compressors is there.Maybe under certain conditions the oil is migrating or being flushed out of the sump while the other compressor is running.Had something like this once, was a b*** to find.

[kkboy]

Is the oil pressure safety an adjustable pressure switch. if so see what it is set at. some people like to adjust them and adjust them the wrong way. Are the compressors fitted with a sump heater and are they workiing as if there is liquide getting back then the sump heater would boil this off. You only say it trips in winter time. Does it happen mainly overnight when the ambient is cold. if this is the case then i would look at your condensser fan cycling to make sure it is not over condensing also. but first would check to see what the oil pressure is set at and adjust if needed.

[ironmen]

HI all,ive seen two tx valve and they was not operating correctly,replaced both.. and im getting a better superheat.its been a week since ive done that and its been working fine i will keep you inform gys.

[sedgy]

well done ironman , stick to it .