Digital Johnson trouble

This doesn't sound like a wiring issue. My controller will sometimes "drift" one degree below the set point, but never as much as 3 degrees. What is your target temp and what differential do you have programmed? Are you saying it drops from 70 straight to 64? What is the actual temp of a bottle of water in the fridge?

 

What's the differential set at? Based on the numbers you provided it may be 3, which means it's working perfectly fine. Also, if you set the differential less than 3, once the cooling element is shut off by the thermostat, at say 65 or 66F, it will still give off cold air and your ambient temp can still drift down a degree or two before it warms up again (esp. if you ferment in a chest freezer). Lastly, minor temp fluctuations of a degree or two for such a short period of time won't effect the actual temp of the fermenting wort, so no worries.

 

Some misleading inuendo in this thread title.

 

Where is the temperature probe?

 

My understanding from the OP's post is that it is supposed to cut on at 67 and then it cuts off at 64. But for some reason it did not cut on at 67. It got up to 70 and when he shook it, it finally cut on.

 

Time to buy the analog controller you should have bought in the first place

 

Having a response by giving it a shake indicates something mechanical at the root of the problem. Could be loose wiring or perhaps a sticky relay (either of which could happen with an analog or digital controller).

 

As long as the temperature is centered at 67, the range you're experiencing (+/- 3 degrees) won't have an appreciable effect on the temperature of your fermenting wort. I've also read that setting the differential to less than +/- 3 can cause your fridge to short out.

 

You need a controller with a variable differential that you can choose. That controller is probably great for cellaring beer in a chest freezer, but the differential swing is perhaps too high for fermentation. You don't want to set it so low that it burns out your compressor from rapidly turning on and off, but you don't want wide swings either. Three degrees is a little high, but frankly should be fine - the wort temps won't fluctuate as rapidly as the air temperature. Two is often the best compromise.

 

His Johnson controller has all of that functionality.



As other people have asked, what is your differential? And where are you placing the temp. probe?

Your differential should be set to 1 or 2°, mine is set to 1°...and your ASD set to 10 or higher. The probe should be taped to the side, and isolated from ambient.

The only time I have had more than 2° temperature swings was when the diff was set higher than 2.

 

Well, the important numbers look good, though I'd set your ASD higher.

If I were you, I'd open it up and check for a loose wire/connection.

 

Thought maybe he had the analog one, A19AAT-2C.

I set the differential to 2 degrees. I use two freezers, a really cheap small freezer and a much larger better quality one. I often take ambient temperature from the larger freezer. It 'll sometimes have more than one fermenter in it and its kind of an art to choose the best temperature, and you need watch the actual temperature in the fermenters. The swing in the ambient temperature is four degrees, but those fluctuations are greatly smoothed within the fermenting beer because its a liquid. In early fermentation, I'll try to use the smaller freezer. I've tried a few methods of probing temperature: a stopper with a thermocouple, the probe taped to the fermenter, and ambient temperature. If I need a 1" blow off tube I can't use the thermocouple.

 

From your description, this most likely is a circuit problem or maybe temp probe problem. No harm in checking the wiring, but I would look for my warranty papers. Did you measure the actual fridge temp (bottle of water)?

 

I'm with utahbeerdude, sounds like the internal relay might be sticking. What model do you have and when and where did you get it?

 

Was gonna say "I never seem to have this problem with my analog Johnson controller."

 

Nah, they're not true relays (magnetic coils and moving parts). These relays are solid state.

 

Yes, the control side is digital, but the 110v side must have a mechanical contactor somewhere (at least the freezer itself), no?