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Setting up Johnson Digital Temp. Controller

Just received my Johnson A419 Digital Temp. Controller. I am going to use it to control my chest freezer for fermenting beer. I am defrosting the freezer right now to get out the ice and clean it up.

The default is set to cold and am looking to keep it at 63 F for now. Do I keep it at cooling? the room temp is 77 F right now. Does any other setting need to be changed from default?

Thank everyone in advance for your responses.


If I recall, we had to change ours to “Heat Mode.” It seemed unintuitive.

I believe “Heat Mode” turns the compressor on when it reaches the upper end of the setpoint, whereas “Cool Mode” turns the compressor off at the upper end of the setpoint.

EDIT: Best way to tell, before you ruin a batch of beer, is to just grip the probe tightly in your hand. Your body heat will heat it up past the set point. If the compressor turns on, then you’re good to go.

If it turns off, then switch the jumper around.

I set the deadband (gap between on and off) to the lowest it lets you, I think its 1 degree. This works for me since my freezer cools much faster than the temperature probe actually responds, so the temp continues to drop after it shuts down, meaning I really have a larger deadband than what I set.

Basically you want your deadband to be as low as you can get away with, and still avoid having it constantly cycle on and off (which will be bad for your freezer).

Other than that pretty sure mine is all default.

I have the same temp controller as you. First of all, you want to insulate and tape the probe to the fermenter once its inside the chest freezer. This way it will regulate the BEER temperature, not the temperature inside the freezer. Your freezer will basically ‘chase’ the temperature you want. It may get a degree or so higher, but it works great. Essentially, think about it this way:

Scenario 1: you want to keep the beer COOLER than ambient air outside the freezer/chamber (most typical). You want the controller set to cooling mode, then plug in the freezer. I believe the instructions refer to this as “cut in at setpoint”. This essentially means that once the probe reads a temperature that is higher than where you set it, the COMPRESSOR will “cut in” and COOL the freezer, thereby cooling the beer.

Scenario 2: you need to get the beer WARMER than ambient air outside the freezer (more for winter time). I have a brewpad (heating element) stuck to the inside of the freezer. You have to switch the jumpers inside the temp controller casing and plug the controller into the heating element (in my case the Brew Pad), as opposed to plugging in the freezer/compressor. This will “cut out at setpoint”. In other words, if you need to keep an ale at 66* in your basement, which has an an ambient temp of 55, the heater inside your (my) chest freezer will run UNTIL the beer/probe gets to that temperature, then it will cut off once it gets there.

They make ‘dual stage’ controllers, where you just ‘set it an forget it’, which is a nice luxury, but the set up you have works great.

Its a little confusing at first, but this is going to make your beer light years better.

Thanks so far fellas, I do have a good temperature gauge inside the freezer to keep an eye on the temp. I am going to plug in the unit and keep it in “cool” mode.

How about the freezer setting, it is currently in the middle (which will freeze to 0 F. )?

Setpoint - 63F
diF (differential) - 1

All the rest default?

Thanks in advance.


Set your aSD to 10. Otherwise, I think everything else can be default.

Set aSD to 10. Now I have to wait for the freezer to thaw a bit more.

I appreciate all comments and tips. Hope this was a worthy investment.


What’s aSD? Not sure I changed that on mine…

Anti short cycle delay, its measured in minutes. Its basically a minimum “off” time required to avoid continuous cycling that will wear out your freezer. I don’t think I messed with mine since the nature of my system keeps short cycles from happening naturally. Doesn’t hurt though.

So far I am on day 1 since turning the unit with the settings. I am currently at 59 deg. and I set the unit for 65 F. Just to test it I held the probe in my hand and once it hit 65, it turned on. The room temp Is still at 77 F. Keeping my fingers crossed I can get to 65 F and sit there.


I’ve read many times that the temp sensor should be attached to the side of the fermenter and insulated from the freezer compartment. If you do that, the beer temperature will fluctuate the full range of the controller - as little as 1 degree for the Johnson digital and 3 degrees for the Johnson analog. If the sensor is in the open space of the freezer, the air in the freezer will fluctuate 1 or 3 degrees and the beer temperature will fluctuate some fraction of the air temperature; the beer will always be “chasing” but never quite catching up to the air temperature and will fluctuate less than if the sensor is measuring the actual beer temperature.

During early fermentation when the yeast is generating a great deal of heat, would the temperature of the beer out-pace the air temperature badly? Or, would the freezer still keep the beer temperature within the range of the freezer air temperature variation?

Am I missing something here?

Maybe we need someone sufficiently dedicated to take beer temp and air temp readings once an hour for the first 5 days of a vigorous ale fermentation for both sensor placements. Volunteers?

It should be pretty easy to track soon.

It should be pretty easy to track soon.[/quote]

Whoah! That looks awesome!

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