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View Full Version : Carrier 30gxn screw- discharge gas therm fail



Octopus
08-20-2009, 09:12 PM
Ok the the back-story is the chiller had 0 maint.

Apparently some retards cleaned the cond "air cooled" coils w/ highly acid coil cleaner and left it on way to long which killed the coil, they prob were messing with the navigator and changed the fan seq. Then attempted jump out the fan relays using misc outputs and then bypassed the hi press sw. and then "not kidding" used a resistor on the discharge temp sens! and dumped the charge via press rlf valves, So new press rlf valves repaired press sw ect ect unit is as it should.

Unit runs for a day or two and goes off on alarm T070 = Discharge gas thermister fail or "its not bad just replaced checked ohm'ed out" or temp >210 deg f for 30 seconds yeah it's that one!

The unit is short about 15/20 lbs making the discharge gas hot but can't add gas head is 250psi r-134a and it's a screw! The coils are as clean as their going to get... Any ideas would be greatly appreciated. YEAH I know they should replace the coils units 5 years old. It's an EXV in the econimizer shells btw, all fans r 100%

Carrier screw chiller 30gxn version 5

suction psi= 70
sat suction= 41.2
Econ press= 67.8
disch psi= 253
sat cond temp= 147.3 F

Discharge temp = 190 deg F <------every once n a while >210 for 30 seconds.

Dallas Duster
08-21-2009, 06:29 AM
What is your:
DSH
EXV%
Are you sure your suction pressure was greater than your economiser pressure?

Octopus
08-21-2009, 06:07 PM
Yes was back today the carrier agrees that the exv is opening so far to cool the motor so no press diff and basically hot gas is going through the whole unit my discharge superheat is 50 deg f, they are just going to have to put new coils in. Unless someone is going to stand there and hose the coils down every time it gets close to 210 heh I would not put it past them. Econ press was 67 psi suction was 41psi can't add more gas liquid already modulating/ flashing, I had also realized there are no compartments in the fan/coil area so b1 compressor coils are ok and the air is moving thru them and not pulling air from the a1 coils that are fouled, in other words the air is taking the path of least resistance making it worse.

Thank you for your reply

Dallas Duster
08-21-2009, 06:29 PM
I had also realized there are no compartments in the fan/coil area so b1 compressor coils are ok and the air is moving thru them and not pulling air from the a1 coils that are fouled, in other words the air is taking the path of least resistance making it worse.



HUH ?

Octopus
08-21-2009, 07:43 PM
The cond coils are shot so no transfer heat across the coils resulting in hot discharge temp and I can't charge the unit anymore to get my discharge superheat from 50 degrees F and the exv is opening up too much to try to cool the motor so everything is out of whack. I'm s.o.l. and need to replace the cond coils

Dallas Duster
08-21-2009, 07:50 PM
How long does it run until the DGT trips it ? Are your oil filters clogging up ?

Octopus
08-21-2009, 08:17 PM
Why do you ask about the oil filters yes they are the drop is about 28 psi which exceeds limit, It runs for about 4 hours then trips.

Dallas Duster
08-21-2009, 08:25 PM
Just curious if you changed the oil filters and if so what was clogging them up?

Octopus
08-21-2009, 08:31 PM
I just took over the job I don't know what might have clogged them up we have scheduled to replace the oil strainer, oil filters, oil and hopefully the coils and replace that refrigerant strainer with a high cap core on the LL.

Dallas Duster
08-21-2009, 08:52 PM
Well hopefully your compressor is still good.

budglo
08-22-2009, 08:54 AM
Just curious if you changed the oil filters and if so what was clogging them up?Those filters should be changed almost on an annual basis.The filtration on those filters are so good that they plug up thru normal use.

freonrick
08-22-2009, 09:43 AM
I just took over the job I don't know what might have clogged them up we have scheduled to replace the oil strainer, oil filters, oil and hopefully the coils and replace that refrigerant strainer with a high cap core on the LL.

If you replace the strainer with a drier core you will have a problem. The strainer was used because the drier core will restrict too much. Some of the chillers used a strainer and a core. If you need to filter the refrigerant do it a different way. You can filter it off to the side like we do on centrifugals. The oil filters was suppose to be changed after a few hundred hours after start up. Alot of them never got done.

budglo
08-22-2009, 11:31 AM
I agree with freonrick,you cant change the strainer and replace it with a drier core.Do you know what the discharge gas thermister is reading when it gives the alarm?Sometimes it hasnt actually failed , but goes out of range.This might be what is happening here considering the history with the coils.

Octopus
08-22-2009, 12:57 PM
Exactly it is not failing it's just over temp I have watched it crawl up to 210 and shut down, as far as the strainers I hear ya well i'll have to put a strainer back in there.

Thanks for the feedback!

Dallas Duster
08-22-2009, 01:36 PM
Have you tried to disconnect the loaders to keep it from loading up to see if it will stay online ?

Octopus
08-22-2009, 01:48 PM
it's a screw chiller so their slides and it has exv's so the scb "screw control bd" would go into alert and shut the compressor down

Dallas Duster
08-22-2009, 01:59 PM
it's a screw chiller so their slides and it has exv's so the scb "screw control bd" would go into alert and shut the compressor down

I think you need to read the manual to figure out what your working on.

Octopus
08-22-2009, 06:29 PM
Why whould i have to read the manual I know exactly what i'm working on it's a screw compressor which varys capacity via slides/ Varry slide position loading ect.... Reads liquid level ect.

Right from carriers manual

Screw Compressor Board (SCB) — The SCB has
8 inputs along with 2 analog and 5 discrete outputs. The SCB
module communicates the status of the inputs with the MBB
and operates the oil heater (30GXN,R only), cooler heater
(30GXN,R only) and oil pump outputs.

ComfortLink Compressor Protection (CCP)
Board — The CCP board monitors the high-pressure
switch status, running current and motor temperature for each
compressor. Each CCP board controls up to 2 compressors.
The CCP board also controls the motor cooling solenoid, oil
solenoid and contactor outputs. A pre-punched configuration
header for each compressor determines the must trip amps
setting. Each CCP board sends the MBB each compressor's
motor temperature, relay status and running current as a
percentage of the must trip amps value. The CCP board also
communicates any alarm conditions as the feedback value.

Capacity Control — The control system cycles compressors,
loaders, and minimum load control valves to maintain
the user-configured leaving chilled fluid temperature set point.
Entering fluid temperature is used by the microprocessor to
determine the temperature drop across the cooler and is used in
determining the optimum time to add or subtract capacity
stages. The chilled fluid temperature set point can be automatically
reset by the return fluid temperature, space temperature or
outdoor-air temperature reset features

I can't just unplug the unloader on a screw compressor slide "cap valve"

Dallas Duster
08-22-2009, 06:47 PM
Why whould i have to read the manual I know exactly what i'm working on it's a screw compressor which varys capacity via slides/ Varry slide position loading ect.... Reads liquid level ect.

Right from carriers manual

Screw Compressor Board (SCB) — The SCB has
8 inputs along with 2 analog and 5 discrete outputs. The SCB
module communicates the status of the inputs with the MBB
and operates the oil heater (30GXN,R only), cooler heater
(30GXN,R only) and oil pump outputs.

ComfortLink Compressor Protection (CCP)
Board — The CCP board monitors the high-pressure
switch status, running current and motor temperature for each
compressor. Each CCP board controls up to 2 compressors.
The CCP board also controls the motor cooling solenoid, oil
solenoid and contactor outputs. A pre-punched configuration
header for each compressor determines the must trip amps
setting. Each CCP board sends the MBB each compressor's
motor temperature, relay status and running current as a
percentage of the must trip amps value. The CCP board also
communicates any alarm conditions as the feedback value.

Capacity Control — The control system cycles compressors,
loaders, and minimum load control valves to maintain
the user-configured leaving chilled fluid temperature set point.
Entering fluid temperature is used by the microprocessor to
determine the temperature drop across the cooler and is used in
determining the optimum time to add or subtract capacity
stages. The chilled fluid temperature set point can be automatically
reset by the return fluid temperature, space temperature or
outdoor-air temperature reset features

I can't just unplug the unloader on a screw compressor slide "cap valve"

Like I said read the manual. I can`t help getting pretty close to the DIY threshold for me.

Octopus
08-22-2009, 07:10 PM
I'm not understanding what your getting at i have had this chiller and all of it's issues figured out since the middle of the thread.



The End

I am not asking for help I have taken care of the problem new to the fourm and not sure how long you guys keep this crap going thats all


ps, I still don't understand why you keep telling me to read the manual. Wierd!

Dallas Duster
08-22-2009, 07:12 PM
I'm not understanding what your getting at i have had this chiller and all of it's issues figured out since the middle of the thread.



The End

I am not asking for help I have taken care of the problem new to the fourm and not sure how long you guys keep this crap going thats all


ps, I still don't understand why you keep telling me to read the manual. Wierd!

I think you are only seeing a piece of the picture. Good Luck with is all I can say!!!!beat22