Homebrewing Blog and Resource

The hobby of homebrewing beer

Digital Johnson Temperature Controller

The most important thing you can do for your homebrewing is temperature control. After you have mastered the basics of sanitation and wort making, extract OR all grain, your fermentation process is going to give you the most bang for your buck on the road to making better beer. Yeast starters and yeast health are part of it, but in this post and video we are focused on temperature control.

The Digital Johnson Temperature Controller (model A419) is very popular among homebrewers. You can find them for $50-$70 bucks at most retailers. Running one of these in parallel with a fridge/freezer or with a heater like the FermWrap gives you control over ambient temps during your fermentation.

In this video, we break down the process of setting your controller to either heating or cooling by swapping the jumpers inside the unit. For everyone that is timid about electronics, or manipulating expensive and complicated pieces of equipment; we break it down into short easy steps.

As a precaution, be sure that you completely unplug the unit before attempting to open up the unit and play with the jumpers. Be gentle with those jump pins. We take no responsibility for you fumbling around in there with fat fingers and breaking something. Get the neighbors kid to do it if you must!

Cheers. BREW ON!


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  1. EmDubeu

    To easily switch between cooling and heading modes I hardwired the posts that you cover with the jumpers with a rocker switch.I then installed the switch on the outside of the controller. I’ll bring it to one of the meeting to show it off.

  2. Glenn

    This video was very helpful, thanks for posting it. The other one you have was helpful too. I read the directions for the J Controller and felt a little confused. I probably would have figured it out, but your info helped shorten the “learning curve”.

    I like the idea of a “rocker switch”. Can you post/e-mail a picture of how you did this? Thanks. –Glenn

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