Trane RTWA

[Emcorman]

I'm having a low evap refrigerant temp fault every once in a while, this chiller runs at 28 degrees, its in a lead, lag setup with another chiller,only one circuit runs at a time,(balanced run time is enabled), they switch chiller lead once a week. The fault is on the b circuit, maybe once every 2 months.
the low temp setting is 2. I checked the slide valve operation and everything seems to work fine, exv is working properly, I increased the exv response time after the first visit but that didnt help, just wondering if anyone else may have had this problem in the past?

Thanks for any advice.

[Tranetek]

Check your sensors for proper readings. Also check them for any reading to ground with a digital meter. If there is any reading to ground they should be changed. This can cause periodic trips.

[FlewtheCoop]

Its an ice machine I'm guessing? Is it a factory ice controller? Check if there's an "ice done" (that's Carrier terminology, i don't know what Trane calls it) contact and its fully functional. It could be just being forced to run when there's not enough charge required on the tanks.

[Hrdworkingacguy]

If its not an ice machine check pressure drop across the evap barrel and make sure you have flow...I would check the approach also...

[Emcorman]

The approach temp on this circuit is about the same as the other circuit, and the other chiller, it runs about 9, its not a ice machine , the other circuit never tripps out, wondering if the slide valve could be sticking intermittedly?
Thanks for the input.

[chad_nc]

I have had this problem before. What I found was there were two airhandlers on this system, a large and a small. The small runs 24/7 and the large runs 6am-9pm mon-fri. When the large ahu shut down there was not enough load on the machine and it would not unload fast enough and trip off on low evap temp. It did this mainly in colder weather 50-60 deg F. What I had to do to correct the problem was shut the chiller down the same time Large AHU shut down and then turn it back on 15 minutes later. I haven't had the alarm since. The machine just wouldn't unload fast enough and that was the cheapest easiest fix there was. Basically what it came down to was the system did not have enough water in the loop. This may not be your problem but worth a check. Hope this helps


Chad

[Hrdworkingacguy]

This might be fixed already but i'm wondering if the machine is designed to run at 28 degrees? or it is running at 28 degrees...Also is 9 degree approach on the evap or condenser side? I would be worried about flow in the evap and pressure drop through the barrel if its evap approach...

I had a rthc last week that since startup wasn't working right...It turned out instead of a pressure reducing station they used a regulator and took out the adjustment screw...suction pressure was 35# and the expansion tank was full to the top...Also they had the valve on the inlet to the evap barrel closed to deal with the higher pressure and it caused the machine to run really low evap temperature...we drained the loop, replace the regulator and valved off the outlet valve and the pressure drop and ewt/lwt as well as the evap ref. temp were right where they should be...

The issue with the above problem was it was washing the oil out of the separator and tripping on oil loss...but it was related to the machine basically freezing up...

[Emcorman]

I changed the sensors and no more faults yet,
Thanks for the input.