Need help on hill pheonix rack system

[tchristian]

I am working on a hill pheonix rack.One compressor on medium temp side keeps over filling with oil.this is the only compressor doing this.I have replaced the oil bowl,check valve on resivor,and replaced float in seperator.Compressor faults out every other day on oil failure at 2:30 in the morning.It is the only compressor that is overfilling with oil so I believe they have to be connected.I have noticed I can not matain oil level in resivor,oil keeps leaving resivor.If oil is going out into system why is it only overfilling the one compressor after a defrost cycle?System has 6 compressors 2 common suctions 1 on 2 low temp compressors and 1 on 4 medium temp compressors.1 common discharge header and 1 common oil return line.All pressures,tempatures,oil pressures,head tempatures,crankcase temps look good on compressors.I am lost on this though I am new to working on racks any help would be greatly appricated.It is a 2 hour drive to this store and I would love to resolve this issue.Thank's Tom

[tranger03]

Tchristian,

I feel your pain on this one. I find oil related problems to be some of the hardest to troubleshoot. My first thought is to check the oil pressure on the comp that keeps failing. You could actually go ahead and check all of them and compare. If this particular comp appears to have low oil pressure, I would pull the oil strainer and clean. Make sure to reinstall pickup tube with slot side down. How big is the reservoir? Three gallons? I am thinking that you might be logging some of your oil in this compressor due to clogged strainer.

[tchristian]

Thank's for your reply.I have checked all 6 compressors and all are reading 53 to 58 delta p.All are copeland discus compressors.Oil seperator is 2 gallon. thanks, tom

[tranger03]

Have you been adding oil to the reservoir or is the oil coming back at some point? What kind of defrost? Are you using a sentronic ops. How do you know that it fails at 2:30? Is the rack tied to a site controller (rmcc, einstein)? I'm assuming you have low load at 2:30 am. Which compressor is this in the sequence? How long have you been experiencing the problem? How long is the defrost cycle at 2:30?

[gerryboy00]

i guess that the compressor (that fills up) is not running and that the oil is comming back from the suction line header is that possible?

[jpsmith1cm]

Moved thread to Refrigeration and Ice Making. You'll get more help here.

[jpsmith1cm]

Now, to the problem.

First, since you're asking for help, you're no longer qualified to determine what is "good" and what is not. Please provide us with NUMBERS.

Have you looked for iced up cases?

[tchristian]

Yes I have added 1 gallon of oil but it keeps leaving resivor so I quit adding.System is on a emerson control system and gives fault and time of fault and it is always between 2:30 and 2:45am everyother morning.It is a sentronic oil switch and it tripps also,The defrost is just time off defrost on medium and hot gas on low temp.This problem just started about 2 weeks ago,about the time weather started cooling off at night.Every morning I have been there the discharge is holding 200psi suction varries with load 63psi or so.Unit has 404a refrigerant,Seems like everytime compressor #3 cycles the oil level rises very slightly,I think the oil is returning through suction but Honestly im not sure.I cant understand why the other 5 compressors are not getting excess oil if it is returning through suction.Compressor #3 runs less than any of the compressors.Again I greatly appreciate your help on this issue.thank's tom

[tranger03]

Tom,
Sorry I haven't been able to get back to you before now, but I have had a little bit of time to think over your situation. It seems as if your compressor issue and oil issue are indirectly related. I would begin by checking the problem compressor for blow by. It may be that you have blow by in the compressor causing it to shut down on the oil pressure switch. If no blow by at compressor, I would check the sentronic sensor to ensure that it is clean. The compressor doesn't typically shut down due to high oil level. At some point the sentronic has to sense low oil pressure to shut the compressor down. As an aside you can utilize equalizer lines on the compressor oil floats to keep the idle compressor from filling up with oil should a shut down ever occur. Also, check the pressure in the oil reservoir to make sure that the reservoir check valve hasn't failed (should be 5 or 20 psig above suction depending on the check valve rating). That's all I can think of for now. Good luck and let us know how it goes.

[gearhead3]

ive actually had this happen almost exactly. when i would get to the site the oil pressure, level and reservoir would all be correct. i would reset sentronic and watch unit checking all operations. i found that the problem was only happening after 1:00am which is when the biggest load was coming out of defrost and also midnight crew was stocking. other techs were under the impression that customers employees were shutting off fans at night because the wif was too cold for them. which i have heard of people doing so. anyways i stayed the night because it also was a 2 hour drive. watched system in defrost and made sure no fans were being turned off. unit was a twin evap walk in freezer. ended up seeing that when coming out of defrost expansion valve on one evap coil was sticking wide open and never closing. replaced expansion valve and problem went away. also found that previous company that installed system 1) was welding with no nitrogen through lines and 2) had cut screens out of expansion valves. this was a month long head ache for our company.

[tchristian]

Valves on compressor leaking by allowing the other compressors on same discharge line to push oil into compressor and overfilling the compressor with oil.in sense turning compressor into like a oil seperator on its off cycle.crankcase did not show a abnormal temp nor did the head.Im not a rack guy but this was a wild problem to figure out.has anyone ever seen this?

[jpsmith1cm]

Valves on compressor leaking by allowing the other compressors on same discharge line to push oil into compressor and overfilling the compressor with oil.in sense turning compressor into like a oil seperator on its off cycle.crankcase did not show a abnormal temp nor did the head.Im not a rack guy but this was a wild problem to figure out.has anyone ever seen this?

I've seen the problem, but I think you've got it a bit wrong.

Valves leak by into the crankcase. This pressurizes it, stopping the rack's forced oil feed, AND, stopping the natural return of oil through the suction line and motor barrel.

Eventually, the oil that is in the crankcase is pumped out and enters the system.

Crankcase goes empty and compressor trips on oil.

Now, the crankcase pressure normalizes allowing the oil that has built up in the motor barrel to drain into the crankcase, showing a much higher than normal oil level.

[steve wright]

I have also had these problems, I have seen valve plate leak during the off cycle and the flow through the compressor acts as an oil trap.

If this is the case you could connect a gauge on the suction service valve and front seat it (make sure compressor is turned off and oil pod closed) and it will quickly rise to discharge pressure.

If that is in fact happening a lot of oil can collect there if there are prolonged off cycles.

As jp said it is also probably holding oil in motor compartment (due to blow by) trips oil lube control too.

Oil problems seem to be the toughest especially hours away.

[markettech]

ive actually had this happen almost exactly. when i would get to the site the oil pressure, level and reservoir would all be correct. i would reset sentronic and watch unit checking all operations. i found that the problem was only happening after 1:00am which is when the biggest load was coming out of defrost and also midnight crew was stocking. other techs were under the impression that customers employees were shutting off fans at night because the wif was too cold for them. which i have heard of people doing so. anyways i stayed the night because it also was a 2 hour drive. watched system in defrost and made sure no fans were being turned off. unit was a twin evap walk in freezer. ended up seeing that when coming out of defrost expansion valve on one evap coil was sticking wide open and never closing. replaced expansion valve and problem went away. also found that previous company that installed system 1) was welding with no nitrogen through lines and 2) had cut screens out of expansion valves. this was a month long head ache for our company.

Based on the information provided, this sounds like the more likely scenario to me.

The crankcase becoming overfull and the pump locking out on oil sound like 2 separate issues with the first being a result of the second.

Unless you've got a suction accumilator on the rack, I'd be looking at the circuits nearest your pump as the culprit.

[WT70]

Just went through all of this after a company did a refrigerant conversion on a Rack. Same time of night every 2 or 3 days there was an oil fail on a particular compressor. What we finally figured out what was happening, oil was logging in a couple of circuits at night due to low refrigerant velocities under low load conditions. This would cause the circuits to flood to the rack due to the insulation properties of the oil and low heat transfer of the evaps. Now, the case would go into defrost, oil is warm that is insulating the sensing bulb from the actual temps of the suction line.. and the circuits would flood hard trying to cool down evaporators full of oil. Now, this would wash oil from the compressor directly under this circuit, which only took about 5 mins after defrost ended. Then the oil would start coming back from the evaporators due to increased refrigerant velocities after defrost. So, everything would look good when a tech got there. Had to actually sit with it and watch it one night.

Ended up changing 37 TXV's, but it's been purring ever since.

Did any of that make sense?

[steve wright]

It sure makes sense to me, a little low ref flow a little oil lodging a little blow by on the compressor equal big oil problems.

I wish we knew what type and size comp he has. It seems it worked fine till now of course could have been a long term prob he has just has gotten involved in.

If it has a helical separator it just will not work at light loads.

[gban]

maybe the oil separator isnt doing its job
We had a very similar issue with a hill rack also about 10 years old. same senario low and med temp setup. off time for med temp and hot gas for low. ran fine for several years and all of a sudden the reservoir was empty and 1 compressor shutting off on oil failure. checked pump pressure when compressor was running 40-45 lb dif. dropped the float in the separator to see if there was a restriction and when we did almost no oil came out. usually if there is a restriction there should be enough oil to make a mess decided that the oil separator was not separating any oil. as soon as we changed the separator compressor running fine we actually had to remove a couple of gallons of oil sinse the oil was to the top sight glass

[dgruber]

TChristian,

Glad to see you posted here for answers. Thanks for posting the solution.

I have been involved with forum since its inception and it has been a wealth of shared knowledge for all of us. Always learning!

Douglas

[evilsanta]

I would check how the suction group is set up depending on the operating system. I have had the same issue with CPC using there enhanced suction mode. If this compressor runs the most and is the only one at times it maybe coming back through the suction.