Mini Chest Fridge to Fermenter Conversion w/STC-1000 - Help Needed

Okay, so I am very impressed with myself (but I am easily impressed) to have found the cool little fridge that is the perfect size for a carboy and blowoff bucket. $100 used - Cheap! The glass sliding doors on top will make it easy to peek in on progress without disrupting the temps. And it will allow me to put a separate thermometer inside to double check.

So then, of course, I got an STC-1000 controller to pimp it out.

Now if I only knew what I was doing... here's the problem: I want to wire the controller directly into the fridge, but I can't tell exactly how to do that from looking at the wiring diagram for the fridge and the looking at the innards.

Here are some pictures - not sure what I am doing yet... but I am not really interested in wiring up the new thermostat to a bunch of ac plug boxes like I've seen elsewhere - I want to rip out the old thermostat and flush mount the new one cleanly.







Existing thermostat. Note that it has an on/off function too: when cranked all the way counter clockwise, it turns all the power off to the fridge




Here's the access panel to the compressor compartment.

Yes, it's a bit of an ugly duckling, but I'll clean it up - I promise! Here's the good stuff:




Refrigerator Wiring Diagram



Existing Thermostat and power light removed from mounting (front)



Existing Thermostat and power light removed from mounting (rear)



Close shot of interior of compressor chamber. The removed thermostat is hanging outside the rounded hole. The existing sensor wire is the thick white/clear one going into the black foamed-in cylinder.


I'll post again when I figure out next steps.

 

Ok, so by reading a whole lotta stuff on posts here and elsewhere, I've learned some things and figured out next steps.

One thing I learned is that generally a red wire is used on internal wiring to indicate a "hot" lead that is switched. In other words, it's carrying current from a black lead (traditionally, the "hot" lead), but it's doing that downstream from some kind of switch. In our case, that switch is the existing analog thermostat.

Analog. Ahem. What does that mean? You remember that really thick "wire" that comes out of the existing thermostat? Well that's a thermal probe. Meaning, it's so thick because it's actually meant to carry the temperature from inside the box back to the thermostat where it likely chills some kind of bi-metal control. Old school.

A word about the wiring diagram pasted to the rear of the fridge. It depicts an Overload Protector (OP) that didn't jump out at me when I was looking into the compressor compartment. From a little light reading about refrigerator circuits, I discovered that an OP is usually attached like a little hump right onto the side of the compressor. It comes just before the compressor in the circuit so that if the compressor overheats, it can shut it down before going all China Syndrome.

The thermostat comes before this in the scheme of things. This was important to my grasp of the big picture in attempting to understand the relatively simple wiring of a fridge.

Anyway, after removing the small internal junction box housing the wiring coming into the fridge, this is what I found:

Existing Fridge Wiring: Left: wiring bundle going to existing thermostat. Ctr: OP Right: Wiring bundle from Wall/plug



Ultimately I was able to simply remove the wires from the terminals on the existing thermostat, and rewire them to the STC-1000 like this:

Red to the #8 terminal
Black to the #1, jumpered to the #7
White to the #2
Sensor wires to #3 & #4

I didn't have to add any new wires - it took all of 10 minutes.

I used a long drill bit by hand and drilled up into the foam insulation inside the front wall. I routed the sensor to the inside of the fridge compartment via a small hole. I drilled through an existing hole in the sheet metal. Doing it by hand insured I was not hitting any coils.

I used a 4" rotary metal cutter (crazy overpowered for this work) to cut a neat rectangular hole for mounting, and then filed it down so I wouldn't lose any fingers working with it. Here's the final product:



Power up was straightforward. The thing started to chill down. Since I had a brewday yesterday, I placed the sensor into a hollow on the inside of a piece of neoprene, and taped that to the side of the 6-gallon primary fermenter.

And here is the Black IPA in the primary with a blowoff tube running into a bucket of sanitizer happily fermenting away just a few minutes later. I can keep tabs on progress, and I have a secondary thermometer just to double check the temps. So far the fridge seems to be cycling the beer temp down, and I figure by morning the it will just about match the air temp in there and the cycling will be minimal.



That's about all. It was ultimately simpler than I thought, and I am really thrilled with the result. So if you see one of these little fridges on Craigslist like I did, don't be bashful - it's really the perfect fermentation chamber!

Now I will get to work on the next one. Yes, I bought two - a man needs more than one beer fermenting, don't you think?