Walk in freezer

[mikeref]

I have an old Zanotti drop in on a freezer room that is giving me grief. No model number available. Single phase compressor, 2 horse power R404a, hot gas defrost. The room external measurements are in metric, 2.4 by 2.6 by 2.4 metres. 150 mm or 6" insulation. Product load is on site pies, pastry, bread and such which goes to the coldroom before being moved to freezer and further chilled to -18*c. Total product load would not exceed 350 kg at any one time.
The catch is, i have looked after this room for around 18 months,and not had the following dilemma.
The system had severe contamination when i first worked on it. Flushed, added a large capacity drier and sucked it dry. (compressor did not have an oil change due to time constraints, which later came back to bite me.) Now, the room fails to go below -12*c, and this is now 18 months later.
All basic checks have been done. ( fans, iceup, clean condenser, door seal, digital temperature reading verses my digital thermometer, gas charge, insulation moisture, evaporator air duct, air flow, drier restriction, digital temp setting, hot gas bypass, doesn't leak at hot gas solenoid....Take a breath.. CPR setting and.. the following:
After reclaiming refrigerant and another change of drier, (this is a cap system BTW,) recharged at .95 KG.
room temp= -8.1
suction= 225 to 240 Kpa, depending on water in burn off tray
Air onto condenser = 35*C
Air off condenser = 44.8 *C
TD across evaporator, only 4.7 *C. Now that is where i've come unstuck!! Why only 4.7*C when i should be getting 6 to 8*C?
My thoughts are: does the compressor have valve problems, or is the ambient + 70 odd percent humidity causing the evap to ice up prematurely over night? I'm stumped on this one :( Mike.

[charlie patt]

has it got two capiliarys or just the one?

[mikeref]

has it got two capiliarys or just the one? Good question. Only way to even see the evaporator is from inside the room. Dismantle the fans and check coil with a mirror only. Have gone down that path before as hot gas had done it's job but a sheet of ice had fallen away from evap and partially blocked airway. Rather difficult drop in to work on.. Mike.

[stufus]

It's Donald Ducked Mike :D
That's 2 replies now.
Cheers
Stu

[install monkey]

mike is it fully defrosting the coil?? before refrig starts? thats 3 replies

[Magoo]

Have you done a pump down into vacuum and watch if it holds vacuum.

[monkey spanners]

What Stu said!

Time to weigh it in and get a new one! Or a propper split system would be better if theres space and the customer isn't a tight arse...

Jon :)

[install monkey]

theres no service valves on them zanotti's

Have you done a pump down into vacuum and watch if it holds vacuum.

[mikeref]

Yep, no service valves or reciever. might have to pull the gas again, fit a hand valve on liquid line and hope i don't back too much liquid in the condenser. Only way to test compressor me thinks.

[monkey spanners]

Pinch off suction line with something like this,

http://www.ams-incorporated.com/imperialpinch-offtool.aspx

Have used it on liquid lines to pump down things that not meant to be pumped down so i could fit a ball valve.

Jon :)

[al]

Yep gotta shut the suction some how mike. is that enough replies now??
al

[mad fridgie]

Yo ho ho!
350Kg may not sound like alot, but if is fresh and not frozen, the wee thing could be struggling along with the high ambient.
So just to satisfy this little brain, you have 2 problems.
One it is freezing Up and second when it is not, it is not coming down to temp?
My gut feeling is that the compressor is just a bit tired. So in this case "if in doubt, biff it out"

[install monkey]

mad, flog him a widget see if u can boost capacity by 25%:D

Yo ho ho!
350Kg may not sound like alot, but if is fresh and not frozen, the wee thing could be struggling along with the high ambient.
So just to satisfy this little brain, you have 2 problems.
One it is freezing Up and second when it is not, it is not coming down to temp?
My gut feeling is that the compressor is just a bit tired. So in this case "if in doubt, biff it out"

[mikeref]

All good replies, thanks. Customer is not tight but i wasn't going to waste his money just the same. Following up on this drop in, it seems the capacity of it at the best of times is only marginally able to do the job. With high ambients and humidity, i think it has lost the plot. Going to pull the gas and install a hand valve anyway. Temp stall out at -12 degrees C, and ventilation over the top of the room is poor. Outside air temp is 28 and on top of the room is 35 C. Going to pull a rabbit out of the hat somehow. Cheers.