oil not mixing

[jebb1]

Hi I have a rack of three bitzer semi hermetic compressors running one freezer room and three poolrooms. The problem I have is the units are tripping out on mechanical oil safety device. The oil levels in the compressors are controlled by trax oil controller. The system is on R404a and is 18 years old.
- Oil pressure across the three compressors is good at positive oil pressure of 35 to 40 psi.

Initially one of the trax oil level controllers would still fill with oil even when sensing full, this has been replaced, and 10 lt of oil has been put into system. Yet again the compressors are tripping on oil safety and the oil separator is showing no oil.
The oil separator does seem to work , as when the outlet of the oil sep is shut off it does fill, when you pump down we seem to get oil coming back to the compressors.
The weird part is on the receiver sight glass you can see about 1cm layer of oil ontop of the refrigerant. And also when the system is not asking cooling and the compressors are idle the refrigerant level in the receiver drops away, even when you pump down the receiver the level in the receiver drops away???? and conversely once the unit starts up the receiver fills up
Please help me find my oil

[HVACRsaurus]

Hi mate,

It may or may not be relavent..

Sometimes when a system becomes low on refrigerant it can "loose" oil (log in the pipework & evaporators)

Then a clever person comes along & says Holy Carp, this system has no oil (& pumps a dozen bucket loads into it)

Then another clever person comes along & says Far Out, this system needs the TX valves adjusted (& then proceeds to twiddle all the tv valves - albeit swimming with oil & not enough refrigerant)

Then, yet a clever person comes along & thinks, well the first guy put in oil, the next guy messed with the TXV's, what can I do..... Maybe refrigerant is the cure!

Suggest making assessment to whether it has sufficient R404a (Just watch out for return of excess oil & floodback issues if you do add refrigerant..)

* Morale to the story; sometimes when a system looses oil what do you put in - Refrigerant!

Ps, may or may not be relavent but have seen "more than once" - all care & no responsibility use only as directed your mileage may vary imho m.o.u.s.e

Pps, some service history might help in knowing what has been happening with the system, further try to find out if / when it was last working properly & what has happened since.. Seriously, one site I know of, whenever there was a problem, the first thing to do was find out what the last person did & then sort out their screw-up..

Ppps, find & fix any leaks..

[RANGER1]

Hi I have a rack of three bitzer semi hermetic compressors running one freezer room and three poolrooms. The problem I have is the units are tripping out on mechanical oil safety device. The oil levels in the compressors are controlled by trax oil controller. The system is on R404a and is 18 years old.
- Oil pressure across the three compressors is good at positive oil pressure of 35 to 40 psi.

Initially one of the trax oil level controllers would still fill with oil even when sensing full, this has been replaced, and 10 lt of oil has been put into system. Yet again the compressors are tripping on oil safety and the oil separator is showing no oil.
The oil separator does seem to work , as when the outlet of the oil sep is shut off it does fill, when you pump down we seem to get oil coming back to the compressors.
The weird part is on the receiver sight glass you can see about 1cm layer of oil ontop of the refrigerant. And also when the system is not asking cooling and the compressors are idle the refrigerant level in the receiver drops away, even when you pump down the receiver the level in the receiver drops away???? and conversely once the unit starts up the receiver fills up
Please help me find my oil

jebb1,
Be nice to know a bit more.
As Hvac suggests, but you should know if everything is working with below questions.
Does oil separator have a replaceable coalescing filter, if so probably need changing.

Does Trax oil return system have a reservoir for excess oil & is it vented to suction line with pressure regulating valve?
If so maybe need setting up or checking.
Any oil return strainers need checking/cleaning?

If liquid migrates or does not pump down & see level increase, is liquid line solenoid/s closing off properly.

Does suction line have slop pot?

Do compressors experience flood backs or continuous foamy oil?

Superheats checked?

http://www.emersonclimate.com/europe/ProductDocuments/CopelandLiterature/C071701_0208_0913_E_RefScrollParallel_0.pdf

http://www.henrytech.com.au/getattachment/32ad4b03-2d49-40cd-98f3-704ca9411c12/Oil-Management-Systems.aspx

[jebb1]

Thanks for your reply. The gas levels are good , the system when running the liquid receiver is a 1/3 to half full. However if this means anything they are only requiring 20% of the rooms on

[jebb1]

Hi Ranger 1,
Just answering some of your questions
The filter looks like it okay as there is a sight glass after it and you can see the oil flowing correctly
The oil sep looks good as if you isolate the oil going to the compressors it will fill quickly. however one week ago when i put the oil in the system it was at least 50 % full and now its 10% full
The system does not have a slop pot yet it has a suction header.
It is mostly coolrooms with one freezer all running off solenoids on the system
It doesn't seem to experience flood backs, no foamy oil, if you open your gauges only vapour. I haven't completed
a superheat test.
It that where your heading with the comps pumping liquid, and does this mean the oil separator can't catch the oil
Is there any other reasons that the oil is not in the oil sep
Also whats with the layer of oil in the receiver
Thanks

[HVACRsaurus]

Hi Jebb,

Only require 20% of rooms

That raises a flag with me / low load operation..

Is there sufficient load to keep 1 compressor running continuously?

[Grizzly]

Hi Jebb.
Listen to your compatriots.
Low load = low swept volumes = no oil returned.
Low load also can mean low Discharge pressure.
Try shrink wrapping your coolers and defrosting them. Followed by oil drains.
Ranger calls it low on refrigerant! I call it low Gas flows either way they are the same.
No recip system functions happily if there are low loads.
Do you ever have LP issues?
Have you ever considered having the cooler coils cleaned?
Your dual operating parameters will not help either.
But Hey Ho!
1 thing at a time.
Grizzly

[Glenn Moore]

Which oil type is in the system, mineral or POE . I sounds like someone has put mineral oil into the system by mistake . Suggest drain all oil and replenish with fresh POE lubricant

[jebb1]

Thanks Grizzly
Discharge pressures are good as fans run off pressure switch ,
I will get the customer to bring on some of the rooms to test if this low load is the fault.
I don't follow the shrink wrapping the evap coils, can you give more info?

[jebb1]

I put poe, not sure what has happened previously

[joe-ice]

Sounds to me like you have a compressor pumping away your oil. I have come across this with compressors with a reed blown or faulty unloader . I would do a pumpdown test or isolate it and close valves to see if suction rises. I would start with the compressor that had the faulty oil level as if it was overfilling it would go up into the head. Another good indicator of a blown reed would be a head plate hotter than the rest. Also dont forget to remove the litres of oil added when the problem is resolved.

[Glenn Moore]

Hi Jebb1
Some years back Bitzer redesigned their oil float adaptor, where the Trax system is fitted. The later design caused the oil unit to vapour lock itself and during the compressor run times oil would simply pour into the compressor and about 5mm above the top of the oil sight glass the compressors motion gear crank and con rods are spinning and if the oil level reaches that point the oil is simply whisked up and excessive oil is sent to the separator. The separator becomes overwhelmed and oil escapes into the receiver and into the coolers. The oil only returns via a defrost, but is quickly returned back to the system.
If you can take out an oil adaptor and post a picture to see which type is fitted and if its properly vented.

[joe-ice]

Thats very interesting glenn ,I came across that problem a few years ago on a new rack with same type compressors . I reckon severe damage would have been done only for the high pressure switches were piped directly into the head cavity.There was so much oil going up to the head it was like a hydraulic lock. The fix for it at the time was to put in bigger oil feed hoses and that worked , maybe increasing the initial flow overcame its ability to vapour lock.

[Magoo]

hello.
apart from all the good information from previous comments.
the dumb question is have you checked the oil suction strainers in the sump after 20 plus years operation . They have a habit of doing strange things at the most un opertune times especially when you are not on site , so will fault on diff pressure. Really frustrating.
just a thought.