This device is crucial for brewing lagers because it works with your refrigerator or chest freezer to keep your beer within a specific temperature range. Controlling your fermentation temperature is important for all beers but especially when home brewing lagers. Watch this video to learn more about its basic features and how easy it is to use. For the full post, go to

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19 thoughts on “How To Use A Johnson Controls Digital Thermostat Control Unit – The Basics

  1. Mark Wood says:

    My understanding is you should set the differential to 10 degrees so as to not over work the compressor.  The temperature of your carboy isn't going to change much in a sealed fridge or freezer.

  2. Jim Lucas says:

    I was looking for references to incorrect readings on my Thermostar Controller. I have it connected to a Thermostar 12" Sensor then inserted into my carboy via the Stopper Thermowell. The controller is registering a temp of about 110F. This is obviously not right – ambient temp should is probably 70F. I'm at stage 3 on a WineExpert Kit and the SG is hanging at .998 (needs to get to .996 or below) so I'm getting a bit concerned. Any thoughts? The Controller and probe are less than 1 YO. Just a bad bit of equipment? The probe or the controller? Suggestions?

  3. Oscar Sandoval says:

    that asd is very important to prevent your equipment from being damaged by your 1 degree diff setting . Your compressor will fail soon if you don't increase your diff and set a 3 to 5 min asd time .I am a service tech who works on refrigeration a/c equipment . I don't know what type of equipment you have but this is not going to work for long if you keep short cycling your compressor. This is Just my opinion take it or not, but depending on the size of your equipment it will cost you money and down time to make repairs when it happens.

  4. John Davis says:

    I used the dial version on a brand new 15 cu whirlpool freezer.  Controller temp set at 65, freezer temp 61.  The freezer keeps running (26 hrs) does not shut off?  Any thoughts?

  5. Alexis Kwan says:

    I'm using the A419 thermostat for one of my fridge and have set the SP to 38 °F & dif to 5. But the fridges temperature is somehow still sitting on between 76 °F to 88 °F. I'm almost certain that its not the thermostat thats malfunctioning but the motor for the fridge it getting old.
    Is my settings for the thermostat correct?

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