RTAA low evap ref. temp. hair falling out!

[allstar08]

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.

[GT Jets]

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.

Do you know when it trips? Start up, unloading, loading...etc...

There are several causes....The EEV is rarely the issue...

A contaminated refrigerant charge can do this...Has anything been replaced before you R&Red the EEV?

How certain are you that the slide valve is not sticking?

Put up some more stats...I love these!!!!


GT

[mustardman]

How is your flow thats where I would start. Sensors and connections next. Does your flow vary possibly under light loads when the air handlers are bypassing. Out there but is your flow switch stuck in the made position allowing the chiller to run with no pump. Only reason I say this is I just found this exact scenario last week. Are you running glycol and have your settings been changed accordingly.

[ChillerWisperer]

I'd concentrate on the slide valve piston. Even if it isn't sticking, it could be loading too fast. Start it up and watch the RLA% in menu 2. If it makes big jumps with each pulse of the load solenoid instead of small incremental increases, then the rings are worn. It would on;y take an hour or so to pull the plate and check. Unthread the nut a little way and screw one of the plate bolts into it. If you're able to easily slide the piston in and out, then the rings are too worn and you need to replace the piston.

[txhvac]

How cold do you get in the winter? If it happens mainly in this season, it sounds to me like you may be cooling the loop only w/ no load. I agree with Mustardman, what kind of valves do have at the air handlers? You got an 80 ton chiller, does the trip follow one particular circuit? Or does it affect both? I think there was a bulletin out on this, I'll check my books. Hope this can help.

[Healey Nut]

Water or glycol ??? Is the ucm set up properly ??? Flow,flow ,flow is it primary secondary ,variable etc etc. Dont blame the chiller look at the whole system and as far as the slide valve , yes its a possibility but just check the amps at start up to see if its starting loaded . Maybe the flow drops off too quickly under low load and the UCM doesnt back the chiller off fast enough and bingo she trips .

[allstar08]

How cold do you get in the winter? If it happens mainly in this season, it sounds to me like you may be cooling the loop only w/ no load. I agree with Mustardman, what kind of valves do have at the air handlers? You got an 80 ton chiller, does the trip follow one particular circuit? Or does it affect both? I think there was a bulletin out on this, I'll check my books. Hope this can help.

I think you may be onto something. There is not a lot of load and there are no valves at the air handlers. The flow stays constant I assume on pressure, 2 chillers in series and vfds on a lead lag pump skid. If there is a bulletin that would be great! Both chillers have had this fault numerous times.

This is a new contract for our company and the only history I have on it is from the B.E. and the fault logs in Summit.

[allstar08]

Water or glycol ??? Is the ucm set up properly ??? Flow,flow ,flow is it primary secondary ,variable etc etc. Dont blame the chiller look at the whole system and as far as the slide valve , yes its a possibility but just check the amps at start up to see if its starting loaded . Maybe the flow drops off too quickly under low load and the UCM doesnt back the chiller off fast enough and bingo she trips .

Good point I will check on Monday. Most people I have talked to about these chillers like them. I don't have a lot of experience with these units so any help is greatly appreciated. Thanks

[acjourneyman]

Also if it starts when OAT is below 50 and it doesn't have VFD on condensor fan it will suck evap down to trip point because of low head pressure.

[txhvac]

I think you may be onto something. There is not a lot of load and there are no valves at the air handlers. The flow stays constant I assume on pressure, 2 chillers in series and vfds on a lead lag pump skid. If there is a bulletin that would be great! Both chillers have had this fault numerous times.

This is a new contract for our company and the only history I have on it is from the B.E. and the fault logs in Summit.

Ok you're regulating flow w/ the pump vfds, you'll need to determine how the vfd's are throttled. I am assuming they're based on temp rather than pressure, because coils are running wild. Check your minimum speed setting on your vfd's & start there. The Bulletin relating to low evap trips is RTAA-SVB07A-EN, it shouldn't pretain to your chillers since yours are 2002 machines(bulletin for 2001). I don't have it on pdf or I'd post it. My opinion is you've got loop issues too cold temps causing your fault, get some more info on the building, check & make sure your chiller is set-up right. You can set the chillers up on chilled water reset, that way you're not allowing your loop temp to drop too low and fine tune it from there. Hope this can help.

[svc]

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.

[jayguy]

...2 chillers in series and vfds on a lead lag pump skid...

how are the pumps switched? on run hours? on a fault? do they slowly ramp down, turn off, then the other one turns on and slowly ramps up?

just more to add to your check list

[allstar08]

Also if it starts when OAT is below 50 and it doesn't have VFD on condensor fan it will suck evap down to trip point because of low head pressure.

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

[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!:D

[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 

[scott_RWS48]

This upload interface is a little clunky. Hopefully the troubleshooting guide uploaded. Hope this helps.

[scott_RWS48]

And another one. Is this panel the older one with the numeric codes? Or the clear L display?

[climpro]

Is this job Mds Pharma ?

[Healey Nut]

And another one. Is this panel the older one with the numeric codes? Or the clear L display


The 80ton RTAA was never manufactured with a numeric code display .
Is posting confidential service bulletins a good idea Scott ???

[scott_RWS48]

They are "GENERAL" Service not confidential. The RTAA is out of production and I'm sure Trane would like to help wherever possible.

I usually jump in one time, and post with as good information as possible, and then leave the thread. I don't have much time to visit here. I want all Trane equipment to work properly, so just providing what I can. I did not download those TSB off the Trane Tech side of the site. He could have downloaded them himself. :)

[jayguy]

And another one. Is this panel the older one with the numeric codes? Or the clear L display?

looks like a confidential service bulletin to me. trane wants all of their equipment running well. but they will not release any confidential bulletins...most confidential bulletins anymore do not contain a lot of "special-super-secret" info...

[scott_RWS48]

LOL...way to go guys, been at Trane a very long time, no need to stick my neck out to help. Don't worry about getting information from this Trane guy anmore. Good job :)

I remember trying this forum years ago and ended up in all these side battles. I realized I didn't need to be in the middle of it. After all I don't need to be. Guess what I did the 1st time is what I'll do again. Say good bye :)

[jayguy]

LOL...way to go guys, been at Trane a very long time, no need to stick my neck out to help. Don't worry about getting information from this Trane guy anmore. Good job :)

I remember trying this forum years ago and ended up in all these side battles. I realized I didn't need to be in the middle of it. After all I don't need to be. Guess what I did the 1st time is what I'll do again. Say good bye :)

if you want your panties in a wad then fine...the questioning of the confidential service bulletin posting was for your benefit. if you really are a trane technician (still anyway) then you are probably violating the 'never tell any of the super secret info' clauses that you signed.

i do not care if any service bulletin gets out...i really don't. but i don't post them because i want to keep my job. if you don't or you are not worried then fine...post away.

[cooolguy]

ok my advice check your

check suction and saturated sensor
check your connectors on the module
circuit unit charge
compressor starts unloaded at around 40 percent should jump up to 60 percent when female is energized
check expansion valve control response

[milkyway]

if you want your panties in a wad then fine...the questioning of the confidential service bulletin posting was for your benefit. if you really are a trane technician (still anyway) then you are probably violating the 'never tell any of the super secret info' clauses that you signed.

i do not care if any service bulletin gets out...i really don't. but i don't post them because i want to keep my job. if you don't or you are not worried then fine...post away.

im not a trane employee, however i am always studying trane ioms and i have been to many traing classes as well a teardown schools., i like sb and i wish i could get some more so when i do go out and work on a machine i am prepared., ,. any input:bhave:

[milkyway]

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

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

hey graham, can u explain this, if temp is cold outside and there is a call for cooling, i know cond fan will come on for cooling the cond, which would drive head and suction down , i know what a vfd does , and i know what fan cycle does., and if oat sensor set correctly,.
idk ., what really is goning on, also the fans are already cycling i think.,
:playing:

[supertek65]

what part dont you understand???:playing:



hey graham, can u explain this, if temp is cold outside and there is a call for cooling, i know cond fan will come on for cooling the cond, which would drive head and suction down , i know what a vfd does , and i know what fan cycle does., and if oat sensor set correctly,.
idk ., what really is goning on, also the fans are already cycling i think.,
:playing:

[Healey Nut]

hey graham, can u explain this

No head pressure = no suction pressure = no oil movement = no chiller ..Done

[supertek65]

hey graham!!!!!!!!!!!!!!!!!!!!!!!

hows it goin??????????????????



hey graham, can u explain this

No head pressure = no suction pressure = no oil movement = no chiller ..Done

[milkyway]

what part dont you understand???:playing:

The vfd compared to fan cycle controls on cond fan motors

[jayguy]

The vfd compared to fan cycle controls on cond fan motors

head pressure controls turn the fan on and off based on a single pressure...in this case head pressure.

the vfd's turn the fans on and off based on the pressure differential between the saturated condensing pressure and the saturated evaporator pressure.

all txv's (mechanical or electronic) are rated by differential pressure (and a few other things). txv's move their rated tonnage based on this differential pressure. no differential pressure and there isn't any refrigerant movement.

if the saturated evaporator pressure drops and the saturated condensing pressure stays the same (because the pressure switches only switch based on a single pressure), then the txv tonnage rating goes up and you can move more refrigerant.

but what happens when the evaporator load goes up? the saturated evaporator pressure goes up, but the saturated condensing pressure stays the same (because of the pressure switches). due to this issue, the tonnage goes down and you can trip due to a heavy load.

by using the differential pressure, you have several advantages.
1. maintains txv tonnage at all evaporator loads and condenser loads.
2. when the saturated evaporator pressure is low AND the outdoor air temp is low (causing the pressure switch to turn OFF some fans), the vfd's would actually turn ON some fans in order to lower the head pressure and gain efficiency (assuming the differential is high enough)

[supertek65]

hey jay
did you get my email?

[Screwit]

Hey mlkwal1,

Follow the attached link to trane.com literature search and under the helical rotary liquid chillers section download the clear language diaplay troubleshooting bulletin. Page 20-21 details the VSF fan control for the RTAA 70-125 chillers which should help you to understand.


http://www.trane.com/Commercial/Uploads/Pdf/1060/rlc-svd03a-en.pdf

[supertek65]

screwit
is that your namne or attitude???

LOL!!!!!!!!!!!!!!!!!!

or are you a screw chiller guy????

just wonderin????????????:munching:



Hey mlkwal1,

Follow the attached link to trane.com literature search and under the helical rotary liquid chillers section download the clear language diaplay troubleshooting bulletin. Page 20-21 details the VSF fan control for the RTAA 70-125 chillers which should help you to understand.


http://www.trane.com/Commercial/Uploads/Pdf/1060/rlc-svd03a-en.pdf

[Screwit]

Supertech 65, hope my attitude does not come across that way - it is certainly not intended - been involved predominately with screw chillers for the last 20 years so thought the name was appropriate.

[supertek65]

LOL!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

absolutely not, i am sure you have a great attitude!!!!!!!!!!!!!

i was just wondering if you had some other reason for the name???:yes:

frank:playing:




Supertech 65, hope my attitude does not come across that way - it is certainly not intended - been involved predominately with screw chillers for the last 20 years so thought the name was appropriate.

[cooolguy]

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?

yes, this is possible done that on a few units.

[milkyway]

thanks jay