Carrier 30gx EXV Trouble

[izombie]

Hi there.
Im working on a twin circuit carrier system on R22. The problem is with the EXV on circuit A, not being able to open more than 19.1%. I have observed this via CCN and the chiller controller.
Using the test feature on the controller, it seems i am able to open the vavle to 100%.

Anyone able to suggest where to look next, as to why the valve will not open beyond 19.1%, which is resulting in a system pumpdown.

Thanks.

[referteacher]

Maybe your problem is the R-22. All 30GX units I've worked on had 134a.

[izombie]

Ahh yes, my mistake sorry. its a 30GB. The name plate and instrumentation indicates R22. :)

[referteacher]

AAAAHHHH, Yes....30GX have 06N screws....30GB have 06E recips. Entirely different animals. Not enogh experience with th 30GB to be of any help. Sorry. Anybody else???

[djken]

What are your operating conditions? How do you know the exv is only opening 19.1%?

[izombie]

Yes, there are 3x recips per circuit.

The system starts up, watching the system controller, and the pc hooked up via CCN, i can see the analog data for circuit a indicating that the EEV is open at 34% for a few seconds, then it falls back to 19.1% and just sits there.

Its a parallel setup, there is another chiller working fine, holding the water temp at 7'c. I switch that one off, let the water climb up to around ~15'C entering. Start the troublesome chiller again, circuit A comp1 starts, it sits on around 20psi back, 150 head. When comp 2 starts, the back pressure takes a dive and the system shuts down on code 48 from memory... ie, low suction superheat. Circuit B runs fine.

I have metered the valve from the carrier exv controller module, all 'appears' ok. I can also hear/feel the valve open and close. Just how far it is opening, is unknown. I am relying purely on the feekback from the controls.

Thanks.

[licensed to chill]

check your refrigerant thermistors for accuracy. Sounds like you are running a low superheat and the exv is throttling down to maintain superheat setpoint.

[referteacher]

AH, Yes, It's coming back to me. Had one once where previous service tech had swapped temperature sensors from one circuit to the other. The lead circuit would come on and run fine. When the lag compressor came on everything went haywire.
Like "licensed" said check your sensors and terminations. Made sure all the "input" is correct to the controls. Better check them against another reliable temperature meter to see if the controls are getting the correct information.

[izombie]

Thanks for your help. Ill check the thermistors first thing on monday morning.

[rob10]

Originally posted by licensed to chill
check your refrigerant thermistors for accuracy. Sounds like you are running a low superheat and the exv is throttling down to maintain superheat setpoint. Carrier has had it's share of sensor problems.

[izombie]

Yes, it was the superheat sensor alright. Nice easy fix too. Thanks very much for your help.

Referteacher, you meantioned that you had worked on the 30 GX's. Have you ever known of an oil PD of 100Psi somewhere btween the internal filter screen, and the oil pressure tranducer, that is not the solenoid?

[referteacher]

Yup........The first ones had ALCO granulated refrigerant driers in the motor cooling refrigerant line. Seems they startcoming apsrt in the R134a and polyol ester lubricant. The granuals make there way through the system and plug up those little oil filters between the two halves of the compressor. After changing oil filters every 100 hours and even changing a compressor, we finally changed out the drier for a SPORLAN solid core drier..... Problem went away.