RTAA 90 Oil Fault Help!

[B1978]

I pulled this from a thread from 2010,

"assuming the oil temperature sensors are correct...you need to look at the saturated evap temp and compressor temp sensors. if they are wrong, then you could flood back (the compressor won't care), however, you will be putting liquid refrigerant into the oil separator. as the liquid boils off, it pre-cools the oil before going into the oil cooler portion of the condensor. this makes the oil temp colder than the saturated condensing temperature...which is the reason for the diagnostic." -JayGuy

[_knight_]

I checked my other circuit (circuit 2) and I am running almost identical pressure/temperatures, the one thing that is different on circuit 2 is the entering oil temp is 140* with a 117* sat. cond temp. Now that seems to me like that would be the one tripping.
I'm also noticing both compressors sweating badly, and both sight glasses are now flashing, when previously they had not been.
Now I don't believe I'm flooding back because I have 14* superheat. Or am I possibly.
Thanks for the reply B1978

[jayguy]

...I'm also noticing both compressors sweating badly, and both sight glasses are now flashing, when previously they had not been.
Now I don't believe I'm flooding back because I have 14* superheat. Or am I possibly.
Thanks for the reply B1978

sweating compressors are not necessarily a good or bad sign...way too much information is needed to determine if it is good or bad in your case. however, your 14F superheat...where is that? suction superheat or discharge superheat? this unit is designed to have 4F suction superheat and unless you have a temperature probe in the suction line refrigerant stream, you really can't accurately determine if the compressor suction temperature sensor is accurate or not. check your discharge superheat...it should be between 25F and 50F in pretty much all cases. you will be at the lower end of the discharge superheat as the compressor loads up.

[milkyway]

Look jay , found ya!! Good job! B1978'found ya

[_knight_]

sweating compressors are not necessarily a good or bad sign...way too much information is needed to determine if it is good or bad in your case. however, your 14F superheat...where is that? suction superheat or discharge superheat? this unit is designed to have 4F suction superheat

The 14 degrees superheat was suction superheat.
I didn't notice any issues with floodback or with improper EEV function, circuit 1 sensors appeared to be reading accurately and the system never did fault during my time checking everything.
There was one bad condenser fan motor, but that was on circuit 2 side. I didn't notice anything major.
The customer did mention that the compressors were replaced a few years ago, should I go ahead and replace the oil filters, or at least check there for restriction?
Not quite sure where to go from this point.

[Nuclrchiller]

The 14 degrees superheat was suction superheat.

That was determined using "your" measurements, right? It looks as though the chiller is indicating suction superheat is 8 F. As Jay says, check discharge superheat. How did you measure compressor suction temperature? If suction superheat is truly 8 F, that is too high. It should be 4 F, as Jay mentioned, although it may "float" a little under changing conditions.

[_knight_]

That was determined using "your" measurements, right? It looks as though the chiller is indicating suction superheat is 8 F. As Jay says, check discharge superheat. How did you measure compressor suction temperature? If suction superheat is truly 8 F, that is too high. It should be 4 F, as Jay mentioned, although it may "float" a little under changing conditions.

Yes, 14 was my measurement. 8 is what the system was saying, and it was staying pretty constant at that. I haven't checked the discharge superheat.
Now I'm getting mixed signals now on whether my issue is the EEV over feeding, under charged, oil restriction, or what. Because the oil fault issue I'm having is due to a 4 degree deviation from the oil entering temp and the condensers saturated temp for 30 mins or more (apparently).
Are the things I'm chasing after helping me get closer to finding THAT issue or are we talking another problem here? I know you all are giving me good advice on what to check, but ultimately I want to get in your head (as scary as it might be) to know the issues we are looking into, and why we are looking into them in reference to the fault I'm having.....sorry for the ignorance here, but my work on these rtaa's has been limited. Thanks for all the replies up til now, it is furthering my understanding on this system.

[Nuclrchiller]

I would definitely look at possible over feeding the evaporator. The cases I have seen like this it caused the discharge temp to be so low you can stand there and hold the discharge line all day if you wanted to. Usually caused by one or both of the two temp sensors (mentioned earlier) reading incorrectly and causing the controls to think suction superheat is too high, so it opens the EXV to bring it back down (to 4 F), when actually suction superheat is being lowered to the point that it is 0 F, and carry over cools the discharge - including the oil in it - then the remaining liquid in the discharge boils off further cooling the oil - to the point it is cooler than the refrigerant. There is another thread here somewhere where Jay has described it really well. I have repeated his explanation to the best of my recollection. Any errors are my own. I suspect the indicated suction superheat you see (8 F) is incorrect and is higher than the actual, causing this sequence of events. Keep in mind all pressure readings seen on the display are not actual readings, but are calculated from the temperature sensors. Looking at the panel and comparing indicated temperature reading and indicated pressure reading is simply verifying that it is converting the temp to pressure correctly - if the temp sensor is wrong both readings will be wrong.

[Nuclrchiller]

I checked my other circuit (circuit 2) and I am running almost identical pressure/temperatures, the one thing that is different on circuit 2 is the entering oil temp is 140* with a 117* sat. cond temp. Now that seems to me like that would be the one tripping.

Think about that. We want the oil to be sufficiently warm to ensure there is no refrigerant in the oil. I think Trane could have worded that diagnostic better, and done a better job of describing what causes it. I believe the primary purpose of it is to alert us of the fact that "hey, the oil entering the compressor is too cool and probably has refrigerant in it". There is no sump or crankcase to return it to, and heat it to chase the refrigerant out, and then send it to the compressor.

[_knight_]

Think about that. We want the oil to be sufficiently warm to ensure there is no refrigerant in the oil. I think Trane could have worded that diagnostic better, and done a better job of describing what causes it. I believe the primary purpose of it is to alert us of the fact that "hey, the oil entering the compressor is too cool and probably has refrigerant in it". There is no sump or crankcase to return it to, and heat it to chase the refrigerant out, and then send it to the compressor.

Thank you very much, that makes complete sense now. Dammit, it took forever to get my mind wrapped around that, so the diagnostic isn't that the entering oil and saturated condensing temps are supposed to be within 4 degrees, they're NOT supposed to be within less than 4 degrees of each other. I'll look more into the over feeding, now that I know what the problem is.....too much refrigerant mixed in with my oil. Thank you so much nuclrchiller.

[R123]

If the circuit isn't overfeeding, you could simply have a restricted oil filter. You said the compressors were replaced a few years ago so the oil filter could have picked up some trash.

[R123]

Now something odd I haven't heard before was happening, shortly after the chiller started up, on circuit 1 I was hearing a very very high pitched buzzing sound (almost not noticeable), happening for about 5 seconds every 20 seconds or so. Not sure if this info will help anyone but I couldn't pinpoint where it was coming from, just that it sounded to be coming from the two unloader solenoids on the male side?

Thats normal. Thats the load / unload solonoid valves pulsing.

[Octopus]

Listen to Jay the force is strong with him.