RTAA low evap ref. temp. hair falling out!

[Healey Nut]

There aren't vfds on the condenser fans, just fan cycle controls based on head pressure

Bingo !!!!!!! Houston we have a problem .

[markj]

Check ucm settings. What is the setpoint? What is the start/stop temperatures. Is it process or comfort cooling? If comfort and below 42 degrees you will see nuisance trips. Fan inverters? Whats the outdoor air temp? Does the chiller have a outside air sensor? Does it have upgraded eproms to control condensor fans better than the previous algorithm? Are the water temp sensors accurate? Water flow ok? Check the IOM for water pressure drop charts. Lots to look at but these are tough machines.

Lota of good advise here. Make sure the eproms have been upgraded.

[klove]

The Bulletin relating to low evap trips is RTAA-SVB07A-EN,......

Anyone have a PDF copy of this service bulletin? I've got a '95 model that trips erratically, but nowhere near enough to catch it in the act. I'd like to see what Trane has to say about the subject if I could.

[r404a]

heard of some process machines having to have a 10 minute time delay installed on the load solenoid on these machines to keep from tripping low evap on cold days. no bulletin or factory blessing...just get by


r404a

[allstar08]

well I went back today, and I took a in depth look at the piping. it is crap! I thought to myself, "who runs chillers in series?" Nobody does! I isolated each chiller independent of each other and ran them one at a time, and no issues. The piping is ran in such a way that you cannot run the chillers in parallel, lame!

These chillers have been in for a few years, could the problem have been that easy?

Thanks for all the help, I still need that service bulletin about the upgraded eprom.

[allstar08]

is the password for the UCM in the IOM?

[txhvac]

well I went back today, and I took a in depth look at the piping. it is crap! I thought to myself, "who runs chillers in series?" Nobody does! I isolated each chiller independent of each other and ran them one at a time, and no issues. The piping is ran in such a way that you cannot run the chillers in parallel, lame!

These chillers have been in for a few years, could the problem have been that easy?

Thanks for all the help, I still need that service bulletin about the upgraded eprom.

The eproms have been upgraded, everything after March 2001. There should be VFD's on the fans closest to the control cabinet. Now if they're set up to run is different story. I guess I missed the part about chillers in series. So you've got two chillers in series, pumps on vfd's, no chilled water valves, & chiller condenser fan vfds not set up or working... I just can't possibly see why you'd trip on low evap!

[MrSlim]

MN: RTAA0804YN01A3D0BD
SN: U02M07829
This thing is driving my nuts. Tied into Summit. Continual low evap ref. temp faults, mostly in the winter months. I have done everything I can think of, from checking the charge to replacing the EEV. Has anyone had this problem?

I get about one fault a month.

(from RTAA IOM):
Low Evap Rfgt Temp - Ckt 1 or 2 CMR a. The Saturated Evap Rfgt Temp - Circuit 1 or 2 dropped below
the Low Rfgt Temp Cutout Setpoint while the circuit was
running for 30 deg F seconds.
b. See the low ambient ignore time on startup.

Yes, I've gotten this fault before and it turned out to be a fan staging problem. I'll post a thread with information from the RTAA troubleshooting manual titled: RTTA - Variable Speed Fan System

[Healey Nut]

He doesnt have inverters thats the problem , cant keep the head pressure up in low ambient conditions .
Running the chillers in series is no big deal as long as they are set up correctly ie first in line 58/48 2nd 48/38 could be for a process application .

[MrSlim]

I've never worked on an RTAA without fan inverters. I understand this is a factory option. Is it possible to add the inverters in the field? And what all is involved?

[Healey Nut]

And what all is involved?


Buy em ,mount em , wire em, programme UCM . Done

[allstar08]

who has the passcodes for these machines?

[scott_RWS48]

Ok, let’s back up.

++--++ Field start up
--++-- Configuratiuon (be careful, know what you are doing!)


Check very accurately the sub-cooling. RTAA chillers need sub-cooling to be correct at full load as per the IOM.

Another area to check is the load-unload and step loader. Insure NONE of the coils are burned out. Also Insure the output (triac) is working correctly and not shorted. In many cases the coil shorts out and then takes out the output board trac.

Be sure (as another person posted) to check RLA on start up. Normal RLA should be 35-38%. If one or more circuits start and transition (assuming Y-Delta) and immediately show 42-48% OF RLA there is no doubt the PID loop for the EXV will not respond well and tripping off on low evap refrigerant temperature will be a frequent event. The best solution is to install a adjustable LPS and set it to 40 PSI. This will allow the switch to trip, (auto reset) which will flood the evaporator, and on the next start the unit will run fine because plenty of refrigerant will have migrated to the evaporator, allowing time for the EXV to catch up on the next start. This is A LOT cheaper than a new compresser.

Understanding the sequence of operation and knowing what options this chiller has is the key. I suggest you look at these items and post back. 4-degrees superheat and 22 degrees for low refrigerant temp trip.

I’m rather busy these days but if I get a chance to look at this post I’ll try to help you further. RTAA chillers of this vintage usually work well but are very temperamental if anything is not working perfectly well. The algorithms developed for this chiller assume everything is working correctly. As soon as a mechanical, electrical issue arises these chillers become problematic.

Good luck 