Walk in Freezer stays at 25F

[300 Win Mag]

Hey Could really use some help on this one. I have a walk in freezer box that won't drop below 15F even after door closed all night. Checked to make sure electric defrost was not running every time i go, it was not on.
Box 12x7x7 R-404A Sporlan TXV FSE-1-ZP
Compressor AHA2478ZXB Condensing unit AHA 2478 XZXBX
Evap Russel AE 26-75-B Installed NEW TXV
Compressor 14 Amps Running Suction at comp 47#
Discharge 270# 6"from compressor 21F 6" past TXV Bulb which is just outside of coil on suct line 15.3F
Discharge 6" from comp 131.5F Ambient entering cond 71.8F Evap air temp in 26.2F out 23.6F Line set 3/8 & 7/8 Approx 12' long & insulated. This was with txv open.

Adjusted txv closed 2 turns:
Suction 42# Discharge 270# Ambient 75.2F Discharge 6" from comp 157 Liquid line after receiver,drier, sightglass, 105F - at txv bulb 12F - suction at 6" comp 23.3F -
Evap air in 26.1F - out 21.0F Defrost heaters off, "see thru clean coils in and out" Suction valve frosting

Seems if i close txv, I Get lower pressures but coil starves, and if i open valve, pressures rise and i can't get down to low enough flash point, no matter what i do, i can't get below 15F. H E L P !!!!
Thanks, Pilotjoe

[gerryboy00]

may the condensing unit be undersized?

what are the specific cond. -10 or -20 SST?

[markwolf]

Not a whole lot of subcooling if I am folowing your post right it's only 5 deg.another name for the txv is a constant superheat valve.....not cold control valve. slow down get out your pt chart set the valve for 20 deg superheat & go back to your subcooling.

[gerryboy00]

http://66.28.63.222/documents/Evap_x_ref_106.pdf


page 7--- rating at -10 and -20

[markwolf]

Good post gerry.a little short on btu's.

[jhd1234]

My 2 cents worth:

First, let me congratulate you on getting good information to work with. I'm assuming this is a normal walk in box, with 4" thick, insulated, prefabbed, metal covered panels that lock together? IOW- this isn't some homebrewed, plywood throw together with some styrofoam stapled on. I looked a quick claculation chart from Heatcraft and with a little interpolating and rounding off, the load for a 0 degree box and normal usage would be about 6700 btuh while the load for heavy usage would be about 8900 btuh [the quick clac charts are based on a 95 degree ambient outside the box]. The evaoporator coil is rated for 7800 buh at -10 SST with a 10 degree TD and 7500 btuh at - 20 SST [same TD]. The condensing unit is rated for 8300 btuh at -10 SST and 5700 btuh at -20 SST. So, put it all together, and I think the equipment was sized for normal usage of a 0 degree box. 0 degrees or a little lower is all you can expect: however it appears that it should pull down to that without much problem, especially with a 75 degree ambient around the box. I'm sure you checked for infiltration including the drain line. The drain line is trapped, right? What about product load? Are they shoving in racks of hot bread or the like expecting it to pull down quickly? What I don't like is the 110 degree condensing temperature with 72 to 75 degree air entering the condenser. I know you have a load on the condensing unit, but I'm suspicious about a 35 degree TD between entering air and condensing temp. You need to get a liquid line temp at the outlet of the condenser coil to see how much subcooling you really have. I'm wondering if you might have non-condensables. I looked up the TXV in my Sporlan book and that valve looks like the best choice. So, do a non-condensables test and let us know what you find. Is this a new problem or has the system performed poorly in the past? The insulation isn't wet? BTW- if I'm reading you correctly, when you went in 2 turns on the TXV, you had apprx. 3 degrees superheat at the coil. I wouldn't call that starving the coil. Am I reading you correctly? Please clarify.

[refer dude 2479]

Did the box work at some point before your were sent out there or is this a new install. If it is a new install you may be a little short on capacity but you should be doing better than you are. If this is not a new install and this is a service call because the system quit working properly then you have to ask your self "Why is the suction so high?" I would suspect a bad compressor. This is assuming proper charge etc. Leave the txv alone. It does not control suction pressure but rather superheat leaving the coil. On a freezer you should be shooting for 8-10 deg at the coil outlet. Possibly as low as 6 if the pipe run is long enough to protect the conpressor from valve hunting during low loads.

[Dowadudda]

Originally posted by markwolf
Not a whole lot of subcooling if I am folowing your post right it's only 5 deg.another name for the txv is a constant superheat valve.....not cold control valve. slow down get out your pt chart set the valve for 20 deg superheat & go back to your subcooling.

You meant to say, get your liquid right first then go take a look at superheat. Right??

[onebadgrif]

try front seating your suction valve . . .see if it will pull down below zero . . . .if not might be bad valves

[k-fridge]

I don't have my reference materials with me but I think you have the wrong TXV on there. That is a one ton valve when you should have more like a 1/2 to 3/4 on it. Also, that is a ZP charge that I believe should have a MOP of 35PSI so why are you running 47PSI back pressure? I think you need to put the right valve in regardless.

Also as previously mentioned, you may have weak compressor valves. Close off the receiver valve and pump the compressor down either holding the contactor in or forcing the pressure control on to keep the compressor running. This compressor should pull well into a vacuum and hold there once you shut the power off.

[Freezeking2000]

I hope it was fixed since 2004?