True prep table

[nickellhead]

I've been working on older true prep table. The evaporator keeps freezing up. I've replaced the cap tube with same size and length and dryer. Ive brazed in access fittings on high and low it's a R134a system. The thermostat went bad on it also so I replaced it. Then I've replaced the evaporator fan too. At start my cabinet temp was 80 degrees. My ambient 95 degrees. My suction was 17 degrees and head 250. Any help would be appreciated!

[VTP99]

Looks like a restriction with that hi of head pressure. Of course if your condenser is plugged you would get the same result.

[nickellhead]

I overcharged it about 4-6oz to get suction up. I'm wondering if I need to shorten length of cap tube to raise suction pressure. It ran good for a week but now froze up again.

[VTP99]

What's the nameplate charge say ?

[nickellhead]

11oz. It's a True TSSU 48-12

[VTP99]

Pull the charge and weigh in the exact amount. Your overcharged.

[nickellhead]

When I first weighted it in my suction was at 3-4psi. That's why I overcharged. Shouldn't my suction on a refrigerator with 134 be around 25 psi?

[VTP99]

Shouldn't my suction on a refrigerator with 134 be around 25 psi?

Well at 26 psig your coil would be 30* add a 10* TD and your at 40* air temp.

[Capz]

When I first weighted it in my suction was at 3-4psi. That's why I overcharged. Shouldn't my suction on a refrigerator with 134 be around 25 psi?

BTDT. You keep charging until the suction comes up near 18psi and before you know it your head is at 250psi. Still a restriction or a new one in the cap tube.

[VTP99]

On a hot pull down it can go low at first.

[2sac]

134a I like seeing 16-19psi on the suction side. Your head is way too high.

[nickellhead]

When I weighted it in I let it cool down but suction pressure nor head changed. It stayed at 3-4&160ish. And it took cabinet forever to get down to 38 degrees. I just don't understand how it's freezing up when I have it overcharged? I'm wondering also if maybe new thermostat is acting up. The probe goes into a well inside middle of evaporator. I've always seen the probes clipped on outside of evaporator. here's a pic of the top of the evaporator.

[VTP99]

What was the head pressure when you first weighed it in ? With a cap tube and no receiver the only place the extra refrigerant could go to was the condenser. This would reduce your condensing surface area. And yes the temp. control cap tube belongs in that well. Take a closer look at the condenser coil to be sure it is clean.

[2sac]

Does this unit have pans on top? If so, are they keeping pans in it overnight or just a cover? Need to keep pans in it.

[nickellhead]

I think their taking the pans out at night. Why does it matter if pans are in there? I will check and clean Condensor tomorrow. Thanks for all your help!! If you think of anything else please let me know.

[2sac]

Pans need to stay in as an insulator. Box will not reach temp and compressor will not stop running. Similar to keeping a door open

[nickellhead]

Thanks 2sac! That may be the problem. Because its lasted all week and then it sees to freeze up the day after they've been closed for two days. I'll definitely check that out!! I know my head pressure is high but just couldn't understand the week of running fine and then coming back after being closed for two days being froze up.

[trippintl0]

Its freezing up because it doesn't ever get the evaporator coil down to the 15*F that its looking for to cycle off, so it runs forever.

Fix the refrigeration problem. Get cap tube specs from True. Replace it and use a C032CAPT drier or the C052-cap-tt-hh drier. Strap cap tube to suction line like OEM. Make sure clean condenser, clean evaporator, good airflow, all fan shrouds in place, etc.

If a larger drier is used you may need to add a couple of ounces over nameplate to compensate.

When you work on this unit, you put your temp probe in the coil and watch how fast coil pulls down. Also if you replaced the OEM evap fan which moves very slow, with a normal 9watt fan, it will move to much air and coil will run warm and can freeze the food.

Good luck. True tech support is helpful and doesn't mind helping you troubleshoot. They know their products very well.

[nickellhead]

Thanks everyone! I will go there this evening and check all of that. Why does cap tube have to be strapped to suction line?

[2sac]

To guarantee subcooled lquid is reaching the coil. Attach what you can to the suction line. This is a must. I usually use silver tape, then wrap it all with foam tape. If you have room, coil up the leftovers in the evaporator rather than the condenser section. I like to coil mine around my Maglite before installing it. looks neat and is compact.