carrier 30gxn chiller

[licensed to chill]

i have a carrier 30gxn174 air-cooled chiller that is alarming on high discharge temperature(>210 degrees)for circuit "a" only. this machine has kicked my ass up and down and i need some advice before a carrier rep comes out to the jobsite and points at the problem and snickers "you big dummy"
checked the following----
1. motor cooling setpoint -- 190 degrees
2. motor cooling solenoid operation --working
3.replaced economizer float valve and weighed in proper charge of R-134A
4. verified no restriction in economizer bubbler tube
5. checked circuit liquid level-- running 1.8 when fully loaded.
6.checked liquid level sensor per carrier manual sensor-- checks o.k
7. pulled and cleaned liquid line strainer
8. verified discharge temp. sensor is accurate per carrier manual. -- sensor checks out normal.
9. verified condenser fans operation and rotation-- all working properly
10. verified compressor was not over amping -- amps normal
11. verified oil seperator heater was not energized 24/7

circuit "A" runs for around 20-30 minutes and discharge temp rises above 210 degrees. discharge superheat high(80)
but discharge pressure normal 130 psi no problems with circuit "B" at all

please help!

[airworx]

make sure condenser coils are clean, all the condenser motors are running, properly charged, plugged driers, motor cooling solenoids are working, economizer, exv is not fouled and the sensors need to be watched. sometimes a sensor will test fine and look ok but will intemitenly fail.

[Edited by airworx on 12-17-2005 at 06:36 PM]

[licensed to chill]

no disrespect airworx, but everything you mentioned has been checked(carefully read thread)

[rob10]

A thorn in the side of Carrier on all thier small tonnage chillers.

[gyhooyabat]

Licensed,
What is the serial number and what version of software is in the machine presently?

Don't take offense but in case you don't know; open the status screen and scroll down to VERS, click enter to see the respective boards. With the selection arrow pointing at the MBB label, push the escape and enter buttons simultaniously and you will see the entire board part number. The last 4 digits are the software version numbers.

We do have some glitches with some software depending on the machines application. Is this machine being used for process cooling? If so, does the machine have low ambient control, economizer cooling and is the machine configured for such an operation?

[licensed to chill]

thanks for the response gyhooyabat.
i checked with carrier and the main baseboard version is current. the chiller is used for comfort cooling at a church. unit does not have any motormasters for either circuit. i set machine to stage "B" compressor on first and it is cool enough outside to keep "A" circuit from staging on. local carrier rep. stumped so now a field engineer from atlanta is set to visit jobsite. i hate to have this machine stump me and then someone else has to come in and troubleshoot.

[floodedstart]

licensed to chill,
I feel your pain. I experienced this same problem earlier this year. All you have to do is increase your flow through the barrel. You are probably only running at about 18% capacity when you hit the alarm right? I watched that thing for hours. My flow was within spec, but on the low end (30gxn160). If i remember right i increased it to 550-600gpm. Check your pressure drop across your evap and plot it on the curve.Carrier tech support was no help on that one. Good luck.

[licensed to chill]

thanks for the rely floodedstart. the gpms have not been checked on the machine since installation but i will check and see where it falls on the flow chart. circuit"B" has no alarms and the discharge superheat is normal so i am cofused on how low gpms will cause the high discharge temps with circuit "A"?

[floodedstart]

Trust me. Increase your flow rate and your problem will go away. when i first got the call it appeared to be only 1 stage aswell but after further investigation i found both circuits were doing it. Chiller starts up at 9%, maybe increases to 18%. Your discharge superheat steadily rises during this time. It took mine 45 mins to finally trip. Its funny how you can find a discharge superheat setpoint but there is nothing the chiller does to maintain this. Give it a try and let me know how you make out.

[licensed to chill]

thanks floodedstart. i will check gpms monday and let you know what happens. i am willing to try anything at this point.

[jon304j]

On some of the brine applications of these machines I have had trouble in the past as well as low load as mentioned above. I agree increase of flow helps as it creates action in the cooler. taking it for granted the software is current as mentioned I have also lowered the motor cooling setpoint as per service eng. in Syracuse and that helped too. I think they have the ability to unload too far with the thermodynamics of there cooler,control sceme, oil sep., and condenser. This will get worse with poor flows, floating condensing tempratures, non H2O applications, and colder processes. Just my 2 cents.

[floodedstart]

licensed to chill,


How did things go?

[licensed to chill]

hey floodedstart,

Checked gpms on chiller and they are within specs.(middle of flow requirements) Funny thing is, the discharge temperature is normal when compressor starts but as compressor loads up the discharge temperature rises also. As the compressor unloads the discharge temperature drops. WTF? The local carrier guy is baffled.
He has a factory manual(that only CARRIER has-- wont give me a copy)and it has some items to check inside the screw compressor(relating to this problem) but he acts a little nervous and is scheduling a carrier engineer to take a look at. I have officially run out of ideas!! My guess is that the compressor will be replaced before it is over with.

If you have any more ideas floodedstart, i'm all ears.

thanks for your responses.