WCEbloke
03-02-2020, 07:55 AM
G'day all,
I've got a curly one here, I've spoken to a few Fridgys now and have had a range of suggestions, come conflicting with others, I thought I might get this communities advice before taking the next step, I've seen there are some very experienced and clever people on this site, There's a bit to try and explain, but lets see how we go;
THE HISTORY:
I'm working on a Trane RTUB-216 chiller using a screw compressor. Last summer we lost a fair bit of oil from the oil gasket. On inspection, I found there was next to no oil in the oil separator or compressor sump (~300ml). There is no sight glass and the oil safety had not tripped. It is very difficult to determine how much oil is in this system once it has run. There is a procedure in the manual on how to check the initial oil charge involving connecting flexible lines and a sight glass to the oil separator. This is meant to only be done when the unit is in vacuum (so no refrigerant is dissolved in the oil), and all the oil is in the oil lines, filter, and oil sump. The name plate states it takes 8 ltrs of oil. I used the initial oil charging procedure in the manual to charge the unit and ended up putting nearly 8 Ltrs in to the system to get the oil separator up to the desired level. The system ran great for a few months until winter and we started getting 'low evap refrig temp' faults. This temp is measure by a probe located just downstream from the EXV and is used to determine the SST for the Trane controller.
This fault has been intermittently occurring (usually in colder morning ambient temps) right through to this summer and I'm now concerned oil has logged somewhere in the system causing the low suction temp. We've still had no oil safety trips and the unit seems to run ok when it does. I've been recording the sub cooling and Superheat and both are fine. Recently I removed the refrigerant again and confirmed that it was not short of refrigerant. I found very little oil in the compressor or oil separator again.
THE QUESTIONS:
Where is the most likely place the oil is sitting right now?
Why is there no oil in the oil system?
Why did it not trip on oil safety when it was running.
Is it possible the oil is being pushed up to the condenser (air cooled, approx 3.5 mtrs above compressor) during pumpdown and then returning on startup through the evaporator, leaving some logged in the evaporator causing the fault?
What methods can I use to remove the oil from the evaporator if it is logged there.
How should I go about adding or checking the oil level on a system like this to ensure not too much or too little oil is added?
THE SUGGESTIONS SO FAR:
-Add 0.95Ltrs of oil to the sump of the compressor (this is the 'initial factory/field oil charging procedure'), recharge it with Refrigerant and test run it. It may have something to do with the head pressure control. (the condenser coil is in poor condition)
-Do not add any more oil, enough has been added last time, the compressor will not be damaged, the oil safety will protect the compressor.
-Change the oil filter.
-The oil is sitting in the condenser.
-Try moving the oil out of the evaporator by turning the water pumps off and flooding the evaporator with liquid refrigerant
-Try moving the oil out of the evaporator by strapping an electric heater to the water inlet pipe
-Try moving the oil out of the evaporator by using the Trane controller to open the EXV 100% and flooding the evaporator.
If anyone has read to this point, good effort!
I will keep yas posted on the progress.
Cheers.
I've got a curly one here, I've spoken to a few Fridgys now and have had a range of suggestions, come conflicting with others, I thought I might get this communities advice before taking the next step, I've seen there are some very experienced and clever people on this site, There's a bit to try and explain, but lets see how we go;
THE HISTORY:
I'm working on a Trane RTUB-216 chiller using a screw compressor. Last summer we lost a fair bit of oil from the oil gasket. On inspection, I found there was next to no oil in the oil separator or compressor sump (~300ml). There is no sight glass and the oil safety had not tripped. It is very difficult to determine how much oil is in this system once it has run. There is a procedure in the manual on how to check the initial oil charge involving connecting flexible lines and a sight glass to the oil separator. This is meant to only be done when the unit is in vacuum (so no refrigerant is dissolved in the oil), and all the oil is in the oil lines, filter, and oil sump. The name plate states it takes 8 ltrs of oil. I used the initial oil charging procedure in the manual to charge the unit and ended up putting nearly 8 Ltrs in to the system to get the oil separator up to the desired level. The system ran great for a few months until winter and we started getting 'low evap refrig temp' faults. This temp is measure by a probe located just downstream from the EXV and is used to determine the SST for the Trane controller.
This fault has been intermittently occurring (usually in colder morning ambient temps) right through to this summer and I'm now concerned oil has logged somewhere in the system causing the low suction temp. We've still had no oil safety trips and the unit seems to run ok when it does. I've been recording the sub cooling and Superheat and both are fine. Recently I removed the refrigerant again and confirmed that it was not short of refrigerant. I found very little oil in the compressor or oil separator again.
THE QUESTIONS:
Where is the most likely place the oil is sitting right now?
Why is there no oil in the oil system?
Why did it not trip on oil safety when it was running.
Is it possible the oil is being pushed up to the condenser (air cooled, approx 3.5 mtrs above compressor) during pumpdown and then returning on startup through the evaporator, leaving some logged in the evaporator causing the fault?
What methods can I use to remove the oil from the evaporator if it is logged there.
How should I go about adding or checking the oil level on a system like this to ensure not too much or too little oil is added?
THE SUGGESTIONS SO FAR:
-Add 0.95Ltrs of oil to the sump of the compressor (this is the 'initial factory/field oil charging procedure'), recharge it with Refrigerant and test run it. It may have something to do with the head pressure control. (the condenser coil is in poor condition)
-Do not add any more oil, enough has been added last time, the compressor will not be damaged, the oil safety will protect the compressor.
-Change the oil filter.
-The oil is sitting in the condenser.
-Try moving the oil out of the evaporator by turning the water pumps off and flooding the evaporator with liquid refrigerant
-Try moving the oil out of the evaporator by strapping an electric heater to the water inlet pipe
-Try moving the oil out of the evaporator by using the Trane controller to open the EXV 100% and flooding the evaporator.
If anyone has read to this point, good effort!
I will keep yas posted on the progress.
Cheers.