Minimizing evaporator coil icing.

[marinosr]

Hi all!

I have a crappy commercial merchandizing cooler that I'm using as a ferm chamber. It works great for fermentation temperatures, but I cold crashed a beer in it for the first time this week, and the evap coils iced up... not terribly but I definitely got about 8oz of water in the pan when I finally let it thaw. I'm worried that this will cause problems later when I want to lager.

To minimize icing, do you think it's better to have the probe on or off of the fermenter when dropping to low temps? I took the probe off of the fermenter when I dropped the temperature because I didn't want to run the compressor too hard. This led to the fridge cycling very frequently for short cycles, and I got to thinking that maybe these frequent temperature swings were at least partly responsible for the fridge icing. Also I have the temperature differential set at 5 degrees F. Should I make that smaller?

Thanks for your advice, refrigeration gurus!

 

[SpentGrains]

Your best bet is to put a small dc fan blowing or pulling air across the coils, and just keep it running 24/7.

Keeps coils from building up ice and stirs the air.

 

[marinosr]

The system already has forced air running over the evap coils, but I'll wire it so that the fans are always on.

 

[raouliii]

I use a TRUE GDM-10 with STC-1000 as my fermenter and cold crash to the mid 30's with no problems. I found it critical that my STC1000 be wired into the cooler such that the evaporator fan is always on. This forces defrosting of the coil while the compressor is off. I would recommend leaving the probe on the fermenter to reduce short-cycling and allow for adequate defrost time.

FWIW, these coolers are generally setup with a constant cut-in control with its probe attached to/inserted into, the evaporator coil. Each cooling cycle includes a defrost period that allows the evaporator temperature to rise to the cut-in temperature in the low 40s before again cycling the compressor on. This results in a very consistent operation even with a lot of humidity constantly re-introduced into the cooler with constant door openings.

 

[marinosr]

Thanks for the info. I'll definitely change the wiring around. so that the evap fans are always on. Unfortunately, this fridge doesn't have a defrost heater or thermostat, so I'm stuck with trying to manually minimize frosting.

 

[raouliii]

I had assumed that you had added a digital thermostat.

No need for a defrost heater. The relatively warm air, forced through the evaporator, is enough to defrost.

 

[marinosr]

I do have a digital thermostat, just not a defrost thermostat to take the coil temp. I think I'll put on a DPST switch so I can have the fans always running only when I'm really dropping the temp, to save a bit on energy and give the fans a rest. Thanks for your insight!