Carrier chiller temperature sensor

[Gary S]

model is carrier 30GX-182-A0493-PEE. runs on R134A. Has 2 circuits. 2 screw compressors
I have to replace the discharge temperature sensor on circuit B of this chiller as it is reading incorrectly and this reading is affecting the discharge superheat and causing the circuit to trip out on low dischargesuperheat.
it is a short temp sensor and doesnt appear to be on a shrader?
whats the easiest way of removing and replacing this part? Do i need to reclaim vapour from the screw compressor?
Thanks in advance for any assistance

[james10]

Order a sensor and strap it to the discharge line using heat sink and lagging tape then Plug the cable in otherwise you need to pull the gas to change it it would be better if you got a water sensor as they are longer and give better contact to the pipe

[Gary S]

is it just the gas in the compressor that has to be pulled? (presuming u front seat both valves) can u send the refrigerant down to the evaporator?

[james10]

You can't pump them down and there is no suction valve you either strap one on or pull the full charge

[Gary S]

holy **** think the charge per circuit is up toward the 100 kilo mark ill check in the morning. Thought i heard from carriers agent technical guy in Ireland u can send refrigerant to evaporator and drop pressure to 1 bar and do it quick?

[Gary S]

i was there fairly late this evening hadnt much time. thought there was a suction valve at compressor?

[james10]

Not possible as you have no way of stopping the gas returning to the comp from the evap, you can try to isolate high side low side then move the gas with a recovery unit to the cond which would take as long as pulling the full charge DON'T be tempted to try to pump down as there is a high risk of shorting the
Comp to earth

[Gary S]

cheers for info James not gonna be easy. you would think changing a temp sensor would be more straight forward. should be able to isolate at this point. ah well

[serviceman]

American models in the sensor is installed in a thermowell, is held with forceps and removed the damaged sensor and there is no need to recover the 134A

[Gary S]

James i got sorted today. there is a butterfly valve under the compressor to isolate the evaporator. I front seated discharge valve and valve after sight glass and using reclaim unit moved all refrigerant from discharge pipe/condenser into the evaporator. only took about an hour then i could safely remove the temp sensor from discharge valve and replace it. wasnt too bad at all.

[james10]

Thanks for the feedback, I work on these units all the time and I've never seen one with a suction valve
think it must be a factory option goes to show you learn something new every day

[Gary S]

kind of easy to miss and its awkward to close/open. its hard to see and hard to turn. when it was opened after work was carried out the screw compressor started turning with the pressure of the gas entering. i had already pulled the 6 fuses for the compressor.