reach in freezer used as cooler

[Sledge]

Hi

I have a customer with a reach in display box, designed as a freezer, but being used as a cooler. Actually I dont have the customer yet, but apparently the company that sold her this unit has been struggling to make it work for 2 years...without success. I have been consulted and will probably get a call this week.

So, I am trying to get my head straight on the issues.

The problem, or so I am told is that it will run ok for about 18 hours and then fail. Evap will be completely frozen up. There is an electronic temp control built-in that also controls the defrost. Defrost is every 4 hours, off cycle, with no heaters. Target temp for displaying cheese etc 4c(37F).

I was able to see the coil, and it appeared that the coil was a low temp coil, with at least 1/4 inch fin spacing. It looked to me like the pan was not draining the water adequately.

Things I dont know:

compressor, refrigerant, tx size, pipe size, SH, air flow, defrost termination.

Any thoughts?

What are the factors around deciding fin spacing on a coil? What should the air flow be for the different fin spacing?

[mecassa]

Hey Sledge, is the evap located on the top or bottom? Static coil or forced air? What is the duration of the defrost? What is the case size? Sounds to me like the defrost duration is short or set for winter time when the air is more dense. How often does the compressor run? I can't say I 've heard of a freezer display case with no hot or elec defrost

[Samarjit Sen]

I feel the reasons could be as follows.

a. Inadequate air flow over the evaporator cil.

b. Defrosting of the coils are not proper.

The coils may be designed for air defrost, but due to inadequate air flow the defrost is not being performed properly.

The above comments are on the basis of your statement that the unit runs properly for 18 hours.

Measure the air flow and chaeck the same as per the face area. Maintain an air velocity of 600 to 700 fpm accross the Evaporator Coil.

[lana]

Hi there,

The thread says "reach in freezer used as cooler", I assume that the system is designed for low temp application and now is used for high temp. This means that the TEV and the rest of the equipment is for the low temp.
What happens is this : the TEV is selected for say -20°C now the box thermostat is changed to +4°C. Because the evaporating temp. is low and on the other hand the door of a cooler is opened all the time you get frost, and lots of it.

Just a thought .
Good Luck
Cheers

[Sledge]

This is a 8-10 foot long display case, with coil in the bottom, forced air fans (4 of them I think) blowing the cold air up the back wall of the unit.

I have been told that there is no defrost heater installed.

TEV is a good question...I am thinking that if the TEV is for a freezer application, I will end up starving the evap, meaning low evap temp, meaning freeze up?

600-700 fpm across the coil? Is that a rule of thumb, or is that for a certain fin spacing?
I thought that anything over 450 fpm would blow the condensate off the coil, but I may be remembering wrong.

I am wondering about the defrost termination, if it is still in use for a freezer, perhaps they are terminating the defrost prematurely.

I am going to check the temperature control calibration. This may be an issue too.

I know this is all guess work at this point, because I havent actually been able to check anything. Despite 2 years of troubles the unit is still under warranty and they don't want to pay me to fix another contractors work...yet.

[Dr._Fleck]

Forget fins, TEV etc, This is a simple defrost problem, find out the defrost termination temp and duration.

Run it down to temp, put it on defrost and watch it... all will be revealed