STC1000 as Freezestat for walk in

[H20ENG]

Hi folks!
I am looking at using an STC 1000 as a freeze stat with an AC. I am helping my brother with a walk in for deer (OK, beer and deer!). He got a nice little walk in for free but the refer was toast. I steered him toward a window shaker but it keeps freezing up. More research shows that the CoolBot uses a freeze sensor. I think this is the key to using a window AC successfully. We have the STC1000 controller coming now for this purpose.

My question to you homebrew gurus that have used ACs for walk ins: What temp do you have your freeze stat set at and at what delay? (We've tried extra fans and dessicant. I'm convinced this is the magic bullet to prevent frost)

For the STC1000, I'm thinking setting it to cooling mode, 32 (0C) set point, and 2 minute delay should be fine.

My thoughts are that STC will always try to cool to 32. The main thermostat will run the unit trying to maintain room temps. When the coils start to freeze, the STC will then reach 0C and turn off. With the AC fan running continuously, it defrosts in seconds. The STC will now read higher than 0C, time out and restart the compressor. This will eventually remove the moisture and room will reach setpoint on the main thermostat.

Should this freezestat be set higher? 1 or 2C?

I'm building an outdoor kitchen with a large DIY undercounter fridge for the kegs so this whole setup will be replicated once we get it right.

Thanks for any tips.
Cheers,
Chris

 

[erick0619]

subbing. i have an ac unit that wont get any use through out winter and ive been thinking of bulding a ferm chamber out of it.

 

[H20ENG]

The frosting will kill you if not controlled. I was going to put a cycle timer on the compressor (the fan runs all the time), but the STC is so cheap. I cant wait to install this STC as I think this will solve that issue once and for all.

 

[atoughram]

Thats how I do it on my ferm chamber. ST1000 as a freeze stat, but a Brewpi controlling the temps. I've got the ST's temp sensor burried in the fins of the evaporator. The temp is set for 0C and it's got a ten minute delay.

 

[H20ENG]

Thanks atoughram for the validation of 0C.
10 mins delay seems like a long time when we are trying to bring the temperature down quickly but would be easier on the compressor once down to temp. Do you think it needs this long to equalize pressures?

 

[atoughram]

Thanks atoughram for the validation of 0C.
10 mins delay seems like a long time when we are trying to bring the temperature down quickly but would be easier on the compressor once down to temp. Do you think it needs this long to equalize pressures?

I havent done any specific testing, I just gave it a wild arse guess! My AC Unit is a 5000 BTU model and I had it freeze up once, but not since I wired in the freeze stat. If you test it and think it can be shortened, share your results!

Here are the pictures of it. The AC unit had mechanical style controls instead of digital and they were much easier to bypass, so the compressor switch is wired on all the time and the Brewpi and STC-1000 control power to the unit.

On the schematic, it shows as an STC1000+ but actually it's a plain old STC1000.

 

[H20ENG]

Thanks for sharing your setup! How far into the fins did you push the sensor? Touching the copper coil or just the fins?

Controller was delivered so hopefully will get to it this weekend. Will update afterwards.

 

[atoughram]

Thanks for sharing your setup! How far into the fins did you push the sensor? Touching the copper coil or just the fins?

Controller was delivered so hopefully will get to it this weekend. Will update afterwards.

I tried my best to get it close to the coil, but I don't think it's touching - It's also important that you mount it low because the ice forms there first. There are videos on Youtube installing a coolbot that helped.

 

[H20ENG]

The controller is installed in series with the main Tstat and is working great to defrost the coil as needed. Thanks for your assistance!