RTAA 90 Oil Fault Help!

[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.

[B1978]

If his oil filter is fouled he will see lower oil pressure. I keep seeing about a 10-15 psi difference between the discharge pressure and the oil pressure. So, when I see 30+ I start thinking change the oil filter. He never listed the oil pressure. After reading all the responses it looks like he could be overfeeding liquid because of transducers not reading accurately?

[R123]

If his oil filter is fouled he will see lower oil pressure. I keep seeing about a 10-15 psi difference between the discharge pressure and the oil pressure. So, when I see 30+ I start thinking change the oil filter. He never listed the oil pressure. After reading all the responses it looks like he could be overfeeding liquid because of transducers not reading accurately?

This chiller doesn't use transducers, it uses temp sensors. He never listed oil pressure and probably didn't check oil pressure. I agree that more than likely he is overfeeding refrigerant. That's why I said if he determines he isn't overfeeding, it could be a restricted oil filter.

[alcomech]

This chiller doesn't use transducers, it uses temp sensors. He never listed oil pressure and probably didn't check oil pressure. I agree that more than likely he is overfeeding refrigerant. That's why I said if he determines he isn't overfeeding, it could be a restricted oil filter.

R123 and B1978 have a good point that the oil pressure needs to be checked. Especially after the system has had a new compressor installed, its possibly that metal fragments are floating around in the system and may have caused a restriction in the oil filter. If its pressure drop is greater than 25 PSI (maybe even 20) it should be replaced because it showing signs that its plugging up. But I would be interested in what you guys are recommending it be replaced at?

[B1978]

Im not a very experienced Chiller Tech, but I like your 25psi number. So say your Discharge pressure is 200, your oil pressure should not be lower than 175. Its pretty painless to change an oil filter, its a 2 hour job even for a rookie like myself. Some sites keep a few extra, with the gaskets on site.

[jayguy]

...If its pressure drop is greater than 25 PSI (maybe even 20) it should be replaced because it showing signs that its plugging up. But I would be interested in what you guys are recommending it be replaced at?

i prefer to use the table in the manual...

as for the pressure drop measurements, there is a tap on the front of the compressor oil filter (that's the 'in') and the tap on the top of the compressor, pointing up, by the solenoids is the 'out' of the compressor oil filter...remember to use 1 gage!

[_knight_]

Thanks for all the great info guys. I did check the top port for the oil filter outlet and it was 215. My head I believe was around 245, so I am running about a 30 psi drop across the filter. I have the filter and gaskets on order, I'll verify operation after that's changed to see if over feeding is an issue. I'll also double check the discharge superheat before/after I change out the filter. Thanks again guys.

[alcomech]

Hey Jay, thanks for the info. You are absolutely right to check that table which corresponds to the 90 ton unit. I didn't realize that there is such a big difference. I have a RTAA 200 which presents an oil alarm if over 27 PSI.

You are the Master!

[R123]

Hey Jay, thanks for the info. You are absolutely right to check that table which corresponds to the 90 ton unit. I didn't realize that there is such a big difference. I have a RTAA 200 which presents an oil alarm if over 27 PSI.

You are the Master!

Actually, you need to be looking at the table that corresponds to the compressor, not the unit. In the case of the 90 ton chiller, it has one 50 ton compressor, and one 40 ton compressor so you need to look at both tables.

Your RTAA 200 is completly different than the smaller 70 to 125 ton RTAA chillers. The larger chillers use a pressure differential switch and it should be set to trip at 50 ±3.

[Iamclayman2000]

I had this problem a few months ago.
It ended up being a bad oil solenoid valve.
The one right above the compressor on the oil line between the compressor and oil filter.

Good luck.

[jayguy]

I had this problem a few months ago.
It ended up being a bad oil solenoid valve.
The one right above the compressor on the oil line between the compressor and oil filter.

Good luck.

OP has a different compressor/system than yours.