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reggie
24-10-2002, 09:15 AM
Can anyone tell me if the following statement is true?
Whilst working on a -20 walk in freezer which had a capillary problem, (Now fixed by exchanging for a tx valve) after consulting the manufacturer he informed me that the cabinet would never reach temperature whilst empty. Obviously id taken the food out whilst it was malfunctioning and stored it in a back up freezer.
He claimed that the return air inside the cabinet would not be enough to bring the coil temperature down. By putting a load on it, ie filling the cabinet space with food the contents would freeze and create less duty for the unit.
How does that work?
Incidentally ive had many empty cabinets down to temperature before in low applications.

Any thoughts appreciated

superheat
24-10-2002, 01:49 PM
My thought would be: huh!
Evap temp would depend on return air temp and humidity. Adding product would not change the air temp. It would add temp sink and increase run time for pull down. After pull down, product would be a temp source to cool the air after say closing the door. Cold product would increase off cycle time.

Dan
25-10-2002, 03:13 AM
A minus 20 walk-in with a capillary tube? I have never seen nor heard of such a beast!

Self-contained reach-ins when empty can short cycle air, however. The top mount evaporators often have angled fans discharging air toward the front of the box and the air returns up the rear of the box. With no product in the box, the air short cycles because there is no wall of product to assist the discharge air to travel the vertical length of the box. The discharge bounces immediately back to the return of the coil.

Thus, you have an active cold area at the top of the box and virtually no refrigeration in the remainder of the box.

The thermostat satisfies, or the low pressure control satisfies before you can achieve gravitational advantage of the cold air in the lower portions of the box.

But walk-ins........ well I just have to think you meant reach-ins.:)

reggie
26-10-2002, 02:35 AM
Dan thanks for the response and your right. I meant reach in not walk in. Id had a few beers when i wrote the post. This cabinet was the standard 3 door upright freezer with a drop in unit mounted on the top.