Instructables

Temperature Control For Freezer or Refrigerator

This instructable covers the integration of a Johnson Controls temperature control into an extension cord with switch and electrical outlet for controlling a freezer. For fermenting beer, a chest freezer is a fantastic platform but the factory controls are far too cold. This controller project effectively overrides those by cutting power to the freezer once it chills to the desired temperature. The controller in this project is further enhanced with a standard electrical outlet and light switch controller.

When the switch is on and the temperature is higher than the thermostat setting, the outlet is powerered. When the switch is turned off, or the temperature drops below the thermostat setting, the outlet is off.

Required tools:
1) Wire stripper
2) Phillips head screwdriver
3) Electric Drill with small drill bit may be required for attaching the controller to the metal electrical box.

The required parts for this project are:
1) Johnson Controls Thermostat control. This particular one is a model A19ABA. This was purchased from ebay for about $19.00.
2) Extension cord. Make sure this cord can carry the full amp load listed on the freezer or device you are attaching to it. Mine is a 12gauge "heavy duty" and can easily handle the current draw of this freezer.
3) A 2 gang metal electrical box. Available at a home center for about $2.00
4) Misc. electrical wiring. Everything in this project is 12-2 residential wiring or ROMEX. You will only need a few short or scrap pieces for this project. You can also clip down a 10" or so piece of the extension cord if you are frugal or don't have ROMEX scrap lying around. If you go that route, then use this piece whenever this instructable mentions your ROMEX wire.
5) 1 electrical outlet and 1 switch. These are available at a home center for $0.50-$1 a piece. You don't need anything fancy here.
6) Switchplate to cover the face. Optional, but better than getting shocked. Get the 2 gang where one side is switch plate and the other is for an outlet like in the picture.
 
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ambiguator5 years ago
I have a slightly different johnson control - 3 terminals instead of 2.
The diagram shows terminals red, blue, and yellow:
red+blue = open on temp increase...
yellow+red = closed on temp increase...
i'm pretty sure this control will work, but i'm not sure how this translates to your schematic. any thoughts?
What model of Johnson Control thermostat do you have?
answering my own question through experimentation:

red+yellow = cooling wires. these complete the circuit if temperature surpasses a certain level.

red+blue = heating wires. (not applicable in this situation. would complete the circuit if temperature falls below a certain level.)

If you live in a cold climate and your fridge/freezer lives in a garage you might want to hook up a reptile heater or other type of heater to keep it from getting to cold. I wish I had one of these.
ClemsonStuart721 (author)  ambiguator5 years ago
Good point. I've seen a lot of different controllers for applications similar to this. Mine would be refrigeration only so the circuit is closed when temp goes over the set limit but there are some that work the other way around. Yours apparently is capable of both. Make sure you get the right controller for your project!
Lots of folks have mentioned finding the Johnson Controls on Ebay for around $15 -$20. The cheapest I can find one for it about $40. Am I looking at the wrong model? Also, there seems to be a TON of different models -- will they all pretty much work? Thanks! Evan
You can "roll your own" control with a thermocouple and arduino for about $20.

This instructable shows you how to do it for $60, but you can get a much cheaper arduino (RBB) and I counted the cost of the relay, outlet and other stuff that's already part of this project.

http://www.instructables.com/id/Make-your-own-programmable-thermostat-with-Arduino/

It might be the kind of thing where you just need to keep an eye out for a good deal. I would caution when looking for different models since some are designed for different purposes other than refrigeration controls. This model was an A19ABA.
Thank you for this hack . . it will save me a good $30! One question -- do I need to use the switch? The alternative would be just unplugging the extension cord when I'm not using the fridge, right? Because the Johnson Controls has an internal swich? Thanks much, Evan
Correct, the switch is a complete override for the Johnson Control and definitely not a requirement. Should simplify the wiring a bit as well.
b2gills5 years ago
Don't run wire out of a hole in a metal box like that, at least use a grommet, those punch out holes are very sharp. Stranded wires like those found on extension cords do not hold as well as solid wires. I would definitely recommend a wire clamp, it will help keep the cord from being pulled out.
Derin6 years ago
Is ROMEX flattish?if so you may get some at Grundfos.I saw some flat mains cable being strapped to a wellpipe for the sump pump down there,it came in a crate marked GRUNDFOS
mycroftxxx6 years ago
This hack also works if you're not brewing beer and just want another refrigerator that is extra-efficient and cheap to run. Nice job laying out the process for those who are not familiar with it!
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