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.

Step 1: Prepare the Extension Cord

Clip off the female end of the extension cord. You may want to save this for another project. Then cut the insulation back a bit and strip the three component wires back about 1".

While you've got the wire strippers out, cut back some of the ROMEX electrical wire the same way.

Step 2: Attach the Control Box

Using a few metal screws, attach the Johnson Control unit to the side of the electrical box to make it easier to handle. I had to use an electric drill and small drill bit to get through the metal electrical box. This may or may not be required in your case.

Step 3: Pull the Electrical Wires

Pull the electrical wires from the extension cord and from the ROMEX 12-2 into the electrical box. I pulled these through the same port and I did not use "plugs" to fill the hole in later. This should not be a problem for this application.

Step 4: Connect the Switch

Connect the black wire from the extension cord and from the ROMEX to the electrical switch. The order is not important here.

If you've never done this before, loosen the screw terminal and form a small hook at the end of the wire you want to connect. Pull the hook down until it is as close as possible to the post of the screw and hold it with one hand while you tighten the screw with the other.

Step 5: Connect the Johnson Controller

Pull the other end of the ROMEX through the hole in the base of the Johnson Controls. If you've got extra wire here, clip it back to only what's needed. Strip away the outside (yellow) insulation and connect the white and black wires to the screw terminals on the controller. Then take the bare copper ground wire and connect it to the green terminal at the base of the controller.

Be very careful with the controller when the cover is off. The temperature apparatus at the top is sensitive.

Step 6: Finishing the Wiring

There are a few steps left to finish up the wiring.

You should attach a short (5") bare copper wire to the ground terminal of both the electrical outlet and the switch. These should be twisted together with the bare copper that you attached to the case of the Johnson Controller and the green wire from the extension cord. Attach a wire nut to the top to keep them together.

The other electrical connections should be made with the 2 white wires (one from the ROMEX and one from the extension cord.) Attach these to the hot and the neutral terminals on the side of your electrical outlet.

The second picture shows the electrical outlet connected and the wire nut attached to the bundle of the 4 grounding wires.

Once the connections are made, screw down the switch and the outlet into the metal box. I typically wrap the outside of outlets and switches with electrical tape when working with metal boxes for safety.

Notice that the extra ground bundle of wires is tucked neatly behind the outlet here.

I attached a rough schematic of the wiring for this project. The cyan is used to represent white wires and green for ground. Ground is sometimes just the bare copper wire and has no coating. Note that where the green ground wires crosses the black at the bottom right of the switch, this is NOT an electrical connection, just a bad schematic.

Step 7: Finish and Testing

Attach the switch plate and the cover to the Johnson Controller.

Now it's time to test it. In the picture below I set the thermostat on the Johnson Control to 60F. As you can see, with the switch on, and a lamp plugged in, the electrical outlet is powered. To test, we'll drop the temperature bulb in a cup of ice water.

Within a few seconds the bulb has cooled to 60F and the controller breaks the connection turning the light off.

When using this with your freezer, you should drop the copper temperature sensor bulb in the freezer and plug it in. Set your freezer on high and set the Johnson Controls unit to the desired temperature.

As always, be careful when working with household current. If you don't understand the steps of this project or feel uncomfortable with them, consult a qualified electrician.

Good luck and happy brewing.
-Stuart