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jayryu
10-04-2011, 10:58 PM
I 've got service call for Walk-in cooler.
Problem: too high box temerature
Symptom:
c/u: water cooled, comp- tecumseh AKA9455ZXD, refrigerants -R502
working condition: suction 48psi(16F), suction temp aft sensing bulb 55.4F ---> sh 39.4F
hp on receiver 265psi(115.7F), actual temp aft receiver 99.6F ---> sc 16.1F
Box temp 61F, set temp 38F
Evap. dT 3.6F

I h've heard the unit had worked very well for years but not from half a year ago.

I did not have enough time to check at that site. I think next time I have to check TXV.
Any idea will be very much appreciated.

jayryu
12-04-2011, 04:45 AM
I am waiting your expertise. Where are all the guru?, I am waiting eagerly.

Tradewinds
12-04-2011, 09:38 AM
Hi Jayryu,
I've had to change all the temperatures over to 'C so I hope my calculations are correct.

R502 is a CFC refrigerant that depletes the ozone layer so the first thing I would do is recommend retrofitting it with a more environmentally friendly replacement.

http://www.hvacrinfo.com/cope_ae_bulletins/94-15.PDF

Your subcooling looks to be ok at 9K but you would be better off reading it before the reciever ie leaving the condenser coil. It should be approximately between 4-8K.

Your superheat seems high at 22K which could mean the expansion device needs to be adjusted.


Being a watercooled condenser, when was the last time the tubes were cleaned? Is it possible the tubes are scaled and the system cannot reject the heat from the evaporator?

jayryu
12-04-2011, 10:42 PM
Hi Tradewinds,
Thank you for your concern. I know it has to be retrofitted to R404a first. The customer does not know about the history of the unit at all. And I have no idea about the actual refrigerant in the system. I only guess it is R502 because some other guy wrote it down on the unit. There is no return call from my customer yet. When I go the site again I will check condenser dT and etc.
In the meantime, would you explain how to clean watercooled condenser tube?
Thanks again.

Gary
13-04-2011, 02:56 AM
My guess would be a partially plugged TXV inlet screen.

jayryu
13-04-2011, 10:50 PM
Thank you Gary,
I am waiting the call from my customer. He is busy or a very stingy. Without customer's call I cannot have the opportunity to check the TXV.

jayryu
22-05-2011, 04:54 AM
Finally my customer gave me to go ahead with repair today. I checked TXV and found it doesn't work at all - that means completely dead. The inlet screen was clean. I recovered r502 and replaced TXV with same type and charged with R404a. Now it works fine. Thanks everybody.

Royal241
22-05-2011, 03:23 PM
If you have an external equalizing valve, see if the equalizing line is frozen, in that case replace it.

monkey spanners
22-05-2011, 04:41 PM
I hope the system has poe oil in it thats ok with R404A and not mineral oil that is common in R502 systems which isn't...

jayryu
23-05-2011, 04:26 AM
The compressor itself was made for R404a/R507(=Tecumseh AKA9455ZXD). The equalizing line was ok, no ice.
That unit has been working for abt. 8 monthes with 55'F box temperture. Design box temp. is 35 ~ 40'F.