Thermostat/Temp Controller Question

HoppyHoppyJoyJoy · 12-06-2007, 01:04 AM

I'm trying to convert my beer fridge into a lagering cooler, but I've run into a problem.

I bought a Johnson Controls A19BAB-3 thermostat unit on e-bay. It's supposed to be adjustable between 30 and 130 degrees, and it probably is, but it only seems to work when the fridge is too cold, and not when the fridge is too warm (it only goes one way).

I know there are temp controllers that you can install from the outside of the fridge, but I'm too cheap to spend the hundred bucks on one, if I can find the right thermostat from Johnson.

Here's a pic of what I have now. It mounts on the interior of the fridge, with no extra probe needed. I wired it into the lines that came off of the original fridge thermostat, with no problem (aside from the fact that this model won't do what I need it to do).

Anybody using a similar thermostat? A part number would be great.

Thanks!

Hoppy

MikeInCtown · 12-06-2007, 01:21 AM

According to the search I did, the Tstat you bought is used in heating applications.

You would need something different than an A-19 sensor.

PDF here: http://cgproducts.johnsoncontrols.com/MET_PDF/125030.PDF

**Bobby_M** · 12-06-2007, 01:49 AM

Yeah, the specs on it say it's for heating (open on rise). You need one that is capable of close on rise or a double throw. You could actually get a 120vac relay with a 120vac coil and a double throw (i.e. SPDT, DPDT) so that you can effectively reverse the action on the thermo. You'd wire the fridge to the normally closed contacts. Wire the relay coil to the controller. When the temp reaches the setpoint it will open and cut power to the relay coil thereby switching the fridge on. When it drops below the setpoint, it will power the relay cutting power to the fridge.

By the way, it's not a problem with the A19 series, it's the letters after that that determine the applicaton. That link only shows the heating applications.

Scimmia · 12-06-2007, 02:02 PM

Ok, here's a quick summary of the Johnson Controls Temperature controller part numbers:

A19BAB-3

A19 is the product line.

The first letter indicates the sensor location.
A = Remote Bulb
B = Integral Bulb
Either is fine, but "B" needs to be mounted inside the unit.

The second letter indicates how the controller resets itself.
A = Fixed Differential
B = Adjustable Differential
C = Lockout on Low
D = Lockout on High
THIS MUST BE "A" OR "B"! When you set the differential, the unit will cycle on and off when it gets to that temperature differential. With "C" or "D", you have to manually reset the unit every time.

The third letter indicates the the operation of the relay and gives you a general idea of how the temperature differential works.
A = Open Low, Standard Differential
B = Open High, Standard Differential
C = SPDT, Standard Differential
D = Open Low, Close Differential
E = Open High, Close Differential
F = SPDT, Close Differential
"B" AND "E" WILL NOT WORK! Open high means that it turns off as the temperature rises, oposite of what we need. Open Low will work fine, and SPDT means that it can be wired either way. Standard/Close differential gives you an idea on how much the temperature has to vary before the controller kicks in. You will need to check the specs of the specific controller you're looking at, but standard is usually fine (3.5F or less in the temp ranges we need).

Everything after the dash indicates the temperature range. You will have to check the specs on that one, I don't have a listing

dontman · 08-28-2009, 09:53 PM

Quote:

Originally Posted by Bobby_M

Yeah, the specs on it say it's for heating (open on rise). You need one that is capable of close on rise or a double throw. You could actually get a 120vac relay with a 120vac coil and a double throw (i.e. SPDT, DPDT) so that you can effectively reverse the action on the thermo. You'd wire the fridge to the normally closed contacts. Wire the relay coil to the controller. When the temp reaches the setpoint it will open and cut power to the relay coil thereby switching the fridge on. When it drops below the setpoint, it will power the relay cutting power to the fridge.
By the way, it's not a problem with the A19 series, it's the letters after that that determine the applicaton. That link only shows the heating applications.

Bobby,

I seem to be in the same boat as the op here. Your post gives me a glimmer of hope but everything in bold reads like a foreign language to me. Are these relays and coils available at a standard hardware store? Around how much?

I have an A19-AAA and it turns on as the temp gets colder

shortyjacobs · 08-29-2009, 12:22 AM

Quote:

Originally Posted by dontman

Bobby,

I seem to be in the same boat as the op here. Your post gives me a glimmer of hope but everything in bold reads like a foreign language to me. Are these relays and coils available at a standard hardware store? Around how much?

I have an A19-AAA and it turns on as the temp gets colder

I THINK you need something like this:
Altronix RAC120 DIN rail mountable relay,120 VAC operation 15 AMP/120 VAC DPDT contacts. 30ma current draw.

To make it work, you'd need two extension cords. Cut one in half, and just cut the hot, (black) wire on the other.

Plug the "male" end of the cut one into your A19, and attach the wires the other end into the "coil" contacts of the relay.

This is how a relay works:
http://www.the12volt.com/relays/relays.asp

Take your other extension cord, (with the cut black wire in the middle), you will need to hook this one into the "normally closed" contacts on the relay. There will be one common contact, one normally open, (NO), and one normally closed (NC). Hook one side of the black wire into the common, and one side into the NC. If you can't figure out which is which, try one....if your fridge continues to operate like it is now, (coming on when it gets cold, not warm), you guessed wrong....use the other one. Good news is, you can't break the relay, (as long as you hook the right wires up to the coil), so sooner or later you can get it!

Now plug one end of the black-cut-wire extension cord into an outlet, and plug your fridge into the other end.

(if you get a DOUBLE-pole double throw, instead of a SINGLE pole double throw, instead of having a common, NC, and NO, you will just have TWO NC and TWO NOs....hook the black wires into the NO contacts)

dontman · 08-29-2009, 03:45 AM

Wow, thanks for the awesomely detailed description. I feel like I could do it now.

Catt22 · 08-30-2009, 09:49 PM

Quote:

Originally Posted by HoppyHoppyJoyJoy

I'm trying to convert my beer fridge into a lagering cooler, but I've run into a problem.

I bought a Johnson Controls A19BAB-3 thermostat unit on e-bay. It's supposed to be adjustable between 30 and 130 degrees, and it probably is, but it only seems to work when the fridge is too cold, and not when the fridge is too warm (it only goes one way).

I know there are temp controllers that you can install from the outside of the fridge, but I'm too cheap to spend the hundred bucks on one, if I can find the right thermostat from Johnson.

Here's a pic of what I have now. It mounts on the interior of the fridge, with no extra probe needed. I wired it into the lines that came off of the original fridge thermostat, with no problem (aside from the fact that this model won't do what I need it to do).

Anybody using a similar thermostat? A part number would be great.

Thanks!

Hoppy

I think I know of an easy solution to your problem. You can modify the controller you have by simply moving the lead to the switch. Just below the temperature dial you will see a small rubber plug. Pull this plug out and it will reveal a threaded terminal. Move the screw & wire from it's current position to the revealed terminal. This will cause the controller to switch on with a temperature rise instead of off as it is now. This mod also works on the more common A419 Johnson Controller. IOW, either can be used for heating or cooling by making this switch.

dontman · 08-30-2009, 11:37 PM

Quote:

Originally Posted by Catt22

I think I know of an easy solution to your problem. You can modify the controller you have by simply moving the lead to the switch. Just below the temperature dial you will see a small rubber plug. Pull this plug out and it will reveal a threaded terminal. Move the screw & wire from it's current position to the revealed terminal. This will cause the controller to switch on with a temperature rise instead of off as it is now. This mod also works on the more common A419 Johnson Controller. IOW, either can be used for heating or cooling by making this switch.

HAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAAAAAAA!!!!!! !!!!!!!!!

OMFG!!! I saw that rubber plug, never thought much about it. Started searching here first and never even looked.

Thank god I did not drive 1.5 hours to go pick up the very overpriced controller today. I was supposed to, didn't feel like it, decided to go tomorrow instead.

You sir, are my new hero. I now have a working thermostat on my fermentation fridge. Yay!

**Bobby_M** · 08-31-2009, 12:26 AM

Wow, that's awesome. Why would they market a heat only unit (and vice versa) if they're all double throw? Goofy.