Temp controller questions

[beninan]

About a 1 1/2 years ago, my dad had bought an old foreclosed convenience store, which has several home-made refrigeration units in it. Today, I scored a Johnson temp controller (model A19ABA-40) for the low cost of free. I know these aren't the greatest controllers out there, but for free I'm sure that nobody could pass it up.

I have been trying to find a spec sheet on it, but can only find info on amperage rating (which is already printed on the inside of the cover). After looking at the rigged up home-made setup on the cooling unit (it was literally an uninsulated kitchen cabinet with an A/C unit from an old city bus, and an external pump inside a different cabinet 5 feet away) it seems that all the temperature controller did was open/close the hot side circuitry. All the temp controllers I've seen online have the "female" and "male" plugs for plugging into the refrigerator/wall. If I were to cut and splice this into the hot side wiring of the refrigerator and mount the controller on the inside of it, would this serve the same purpose as the male/female plugs? Anyone have any warning against doing so?

 

[PT Ray]

You got it. It basically switches the hot side off and on like a light switch. You can splice an extension cord or hard wire it like you said.

 

[beninan]

Ah thanks. I think I'll splice it into the refrigerator wiring, it seems simpler and and probably would require less parts.

 

[PT Ray]

I just remembered wiring up one of this inside a friend's fridge years ago. I actually pulled the original t-stat out and wired that in it's place. It's a mechanical unit so it doesn't require it's own power. Mounted it on the inside wall of the fridge so the outside still had a clean look. Just had to reach inside whenever you wanted to adjust it. And it left the freezer to operate as normal.

 

[beninan]

Just a word of caution to any future temp controller purchasers- I just did some testing on this temp controller, and found that it opens the circuit on the decrease in temperature, so just the opposite of how the one in my refrigerator operates. When the refrigerator warms up, it shuts off the power. When it cools down, it turns the power back on. I guess this is some important information to know before purchasing one, good thing mine was free. Oh well, it looks like there's no easy plug-and-play way to set it up without adding a relay into the system. I'll have to take a look at the refrigeration unit this came off from to see how it operated exactly.

 

[Catt22]

Just a word of caution to any future temp controller purchasers- I just did some testing on this temp controller, and found that it opens the circuit on the decrease in temperature, so just the opposite of how the one in my refrigerator operates. When the refrigerator warms up, it shuts off the power. When it cools down, it turns the power back on. I guess this is some important information to know before purchasing one, good thing mine was free. Oh well, it looks like there's no easy plug-and-play way to set it up without adding a relay into the system. I'll have to take a look at the refrigeration unit this came off from to see how it operated exactly.

Maybe not. The internal mechanical switch is a double throw type. You only need to switch one of the leads to the opposite terminal in order for it to operate in a cooling mode rather than a heating mode. Here's how to do it.

Remove the cover and you will see the switch inside with one black wire and one white wire attached with screw terminals. There are actually three terminals. The unused terminal will be concealed by a small plastic plug. With your controller configured for heating, the black lead should be connected to the center terminal. This is the lead you want to move to the top terminal. Leave the white lead where it is and put the plastic plug into the center terminal. Now, the controller should close the switch (power on) with a temperature rise instead of opening it (power off).

I have heard that some of the older Johnson analog controllers do not have a double throw internal switch, but I have never seen one of those. I have three of these units and they all have the double throw switches. I use one for heating a fermentation chamber in the winter and swith it back to cooling mode in the summer. Changing the lead should take you about 2 minutes and 30 seconds if you are really slow. Hopefully, you will have one of the units with the double throw switch. Please report back and let us know if this mod works for you. Also, unplug everything before you work on it. You knew that though, right?

Note: I just read your last post again and I think you have it mixed up a little. When in cooling mode, the controller should cut-in when the temperature reaches the set point and cut-out when it reaches the set point minus the differential (which IIRC about 3 degrees for this unit). ie, if you set the dial to 40F the controller would turn on the fridge when the temperature reached 40F and shut it off at about 37F. The differential is pre-set and not adjustable on the Johnson analog controllers. Also, don't sell these units short. They are rugged and reliable and have been in production for a very long time. I have one that I've been using for almost 10 years and it shows no sign of failing anytime soon.

 

[beninan]

Maybe not. The internal mechanical switch is a double throw type. You only need to switch one of the leads to the opposite terminal in order for it to operate in a cooling mode rather than a heating mode. Here's how to do it.

Remove the cover and you will see the switch inside with one black wire and one white wire attached with screw terminals. There are actually three terminals. The unused terminal will be concealed by a small plastic plug. With your controller configured for heating, the black lead should be connected to the center terminal. This is the lead you want to move to the top terminal. Leave the white lead where it is and put the plastic plug into the center terminal. Now, the controller should close the switch (power on) with a temperature rise instead of opening it (power off).

You're Awesome!

I've had it open for a while now so I could Ohm the terminals that were connected to the other refrigeration unit (the top one and the bottom one, my dummy plug was in the middle). Those were the ones that were open on temperature increase. I did notice that plug you mentioned when I first opened it, but I initially thought the unit had an internal circuit breaker and that was the reset button, so never thought anything of it. I took that plug out of the center terminal and checked resistance between that and COM and sure enough, it will work just how I want it.

Also, unplug everything before you work on it. You knew that though, right?

No worries about unplugging everything. I work with computer controlled systems on Ford vehicles, so electrical is second nature to me.

Note: I just read your last post again and I think you have it mixed up a little. When in cooling mode, the controller should cut-in when the temperature reaches the set point and cut-out when it reaches the set point minus the differential (which IIRC about 3 degrees for this unit). ie, if you set the dial to 40F the controller would turn on the fridge when the temperature reached 40F and shut it off at about 37F.

Sorry, when I said, "When the refrigerator warms up, it shuts off the power. When it cools down, it turns the power back on." I meant that's the way it would operate if I hooked up the temperature controller to the refrigerator incorrectly wired.

The differential is pre-set and not adjustable on the Johnson analog controllers. Also, don't sell these units short. They are rugged and reliable and have been in production for a very long time. I have one that I've been using for almost 10 years and it shows no sign of failing anytime soon.

Mine does have an adjustable temp differential, although it seems like the lowest it goes is a 5 degree difference (I may be wrong, it may be less than that), but I can also increase it to about a 20 degree differential, though it seems pointless for my application.

Again, you are awesome, and Thank You
Now my free temp controller has re-become awesome!

 

[Catt22]

Good to hear that you got it working the way you want. I discovered that little trick while attempting to hack it to operate a heater. I was quite surprised when I found that hidden terminal and discovered it was actually a double throw switch. No real hacking required at all and just as easily reversible. I was not aware that some of these units have an adjustable differential. Mine don't, but that hasn't been a problem at all. Brew on!

 

[beninan]

Wow, I feel dumb, maybe I've had one too many....

So now after looking at this temperature controller again, I figured out it was correctly wired the whole time, and if I just installed the damn thing into the refrigerator it would have worked fine. My mind didn't even take into consideration that the controller is sitting on my desk at ambient air temp, and no matter how far I turn down the temp dial, of course it will close the circuit (due to the controller sitting at ambient temperature).

Anyway....here's a picture of the temperature differential control lever. You may have one, its not labeled as anything except "min" and "max".
This is the temperature differential adjustment lever:

 

[Catt22]

I just took another look at mine. It has the Max/Min hash marks on the back plate like yours does, but there is no lever extending out of the slot. It's a slightly different model is all. Otherwise they appear to be nearly identical. Thanks for taking the time to provide the pic.