Help with Johnson Control Unit

I bought the A419 digital control unit that I think a lot of people on this forum have, to attach to a barely used chest freezer. I adjusted the set temperature to 65 and the differential to 3 degrees (latter was the default). When I hooked everything up, the temperature was 75 degrees. I went down to check it out after awhile, and freezer was turned off but the reading on the control unit was 55!

Is there something really obvious I am doing wrong? Let me know if you need more information to answer my question.

 

Hi

It sounds like you have the probe hanging in air inside the freezer. Tape it to the wall and things will work better. You will have to set it a bit below your target temperature, but the probe will be out of the way.

Bob

 

You could install a thermowell, that way it will stay put and you won't get the nuisance readings. I happen to have access to many JCI parts and have a few laying around if you want one I'll be glad to hook you up.

PM me your address and I'll send it out

 

That would be awesome, thanks. PM sent.

 

Hi,

I'm
About to install mine soon actually. I'm guessing I want this set to cooling mode. Correct?

 

Never mind haha I figured it out

 

Yeah, the instruction manual shows how to customize the unit in a number of ways, but I think the default settings (at least for the internal jumpers) are appropriate for what most people on this forum are using it for.

 

Yeah I'm using it for a keezer so I'm going to go cooling mode. 12m cycle delay, 40 f set point, 3 f differential, cut in. The only thing I don't really understand fully is the OFS. Any help here?

 

Here's my version of a homemade thermowell. I filled an old hot sauce bottle with water and drilled a hole in the cap. Free, easy, and works really well.

If I've got a beer that's really going crazy, I'll also do the tape-bubble-wrap-to-the-fermenter trick.

 

I am not an electrical engineer, but from my reading of the manual, I think that is only relevant if you connect your own circuit, like a timer, to the controller. I'm not sure how or why a brewer would use that, but if anyone can help me out, that would be awesome.

 

I would think the OFS "offset" function would simply shift the set point vs the probe reading, perhaps to account for probe/sensor error. Shouldn't be hard to give it a try by changing it from the factory default zero setting to a few degrees and see what happens...

Cheers!

 

Hi

OFS is the offset between your probe and the number the calibration lab gives you when they calibrate your controller. No cal lab - no number - ignore OFS. Just adjust the controller so the delivery temperature is what you are after.

I'd tap the probe to the wall of the keezer and ditch the water bottle. I'd also drop the set point a little. Beer stores the longest below 38F. Deliver temp will always be higher than storage temp...

Bob

 

Thanks! I'll most likely drop the set to 38 with a 3 deg diff

 

I'm questioning the recommendations to use a separate thermowell in a Fermenter. Assuming that a setting of 65 means that this is a fementation chest and not a kegerator. The examples given to place the temperature probe into a liquid vessel other than in the beer itself would lead to lag and large temperature swings. Bob's suggestion to tape it to the carboy or bucket directly is a good suggestion. I use a stickon temperature indicator on all of my vessels, and then separately regulate the ambient temperature via the probe and controller. With a narrow deadband the air temperature should be steady. I monitor the process daily and adjust the temperature setting appropriately. Often I will set 2-6 degrees low to compensate for the heat build up in the beer.

Tony

 

Which Bob was that? The Bob post I read advocated taping the probe to the keezer wall...

Cheers!

 

I should have also mentioned that when I use the probe in a small bottle of water, I set the differential to only 1 degree. In my small chamber, I find it helps prevent short cycling, even with the anti-short cycle circuit built-in. I figure if a container with 4 oz of water changes 1 degree, the container with 5 gallons will barely change temperature ( with each cycle - it will definitely change over time).

That being said, I do wrap it to the side of my fermenter when I first start fermentation. I move it to my "thermowell" once most activity is gone. Definitely more than one way to skin a cat.

 

Fair enough, i read past that. I don't think the wall of the keezer would be a good choice. I specially if it is a cooling wall. I would expect the system would cycle like crazy.

 

That would be my take as well.

In both of my ferm fridges and my keezer, I always strap the temperature probes to the carboy or keg with a chunk of 1" thick closed cell foam over it.

No short cycling, and excellent control of what I actually care about: the beer...

Cheers!

 

The smaller the better, but it should be understood that the insulating effect of the liquid and container itself will indeed "prevent short cycling", but will introduce lag in turning off a cooling cycle. By the time the cooling is sensed in the small bottle of water, the rest of the chamber has overshot the target. The indicated temperature will continue lower than desired. The larger fermentation container will not experience such a large swing internally, but it will be in a cooler than desired environment. I personally aim for more smaller temperature cycles. As long as your not overworking the compressor, odds are low that you actually are, you would be fine. How many cycles per hour are you seeing? Too many expand the dead band slightly. I think you will be surprised.

 

Just wanted to update this thread. Thanks to the generosity of Jdk261, I have a thermowell that I attached to my probe. I never got a chance to test this with beer in it before using the thermowell. However with the thermowell, the carboy I am fermenting my lager in seems to stay at a constant temperature. I did change my offset to to 1, but it doesn't seem to cycle on frequently.