Problems with Johnson Temperature Controller A419

[ohill1981]

Hey folks. I have been having a slight issue with my Johnson Controller. I am hoping to use it as a fermentation chamber for some up coming brews, but can not seem to get the temperatures to stay consistent. I have the Target temperature set at 68F with a Differential set of 2 degrees. The Problem is the freezer keeps getting 7 or 8 degrees colder that the temperature i set it at. This would not surprise me if it was 40 or 50 F in my garage , but it is in low 80's. I also noticed that the freezer is not on while it is this cold. Am i missing something with this controller?

 

[zachattack]

Are you measuring the beer temperature or the air temperature?

Chest freezers have no fan to circulate the air, and the walls are the part that does the chilling. Is the probe just suspended in the air? The walls of the freezer are getting cold, then the air is getting cold, then the probe is getting cold. So at the point when the probe hits your desired temperature, there's still a good bit of momentum and the probe temperature will continue to drop. Chances are, something with a lot more thermal mass (like a keg or full carboy) will see a very small temperature change during the cycle.

For a keezer, you adjust for this by setting a higher differential and/or tape the probe to something with a good bit of thermal mass.

For a ferm chamber, you need to be measuring the beer temperature, not the air temperature since the fermenting beer can easily be 5 degrees above the ambient air temperature. Try taping the probe (with a little bit of insulation over it) to the outside of the carboy.

 

[brent77]

I had a similar issue. Make sure you secure the probe to your fermentation vessel, and then insulate over it so its only measuring the temp of the beer. Better yet is to get a temperature probe bung. Those produce the most accurate reading.

As for the temperature swing, this could be (as it was with me) that the pins inside the box are set for the heating mode, and not cooling. For some reason It doesn't register the threshold the same way going up as down.

 

[ohill1981]

Thanks so much for your response and i apologize for the delay in mine. I was measuring just the air temperature. I appreciate you both explaining the process to me. I will try adjusting the differential and also fixing the probe to the carboy. I am slightly confused on what type of insulation you are referring to however? Would some light foam work ? or is there something i could use that would work better?

If im understanding you guys correctly the goal is to isolate the probe from the air in the freezer and get strictly a vessel/beer temperature ?

 

[zachattack]

For fermenting beer, yeah you definitely want to isolate the beer temp. For insulation, some bubble wrap will work, or a bit of cloth, anything really. Sounds like you're on your way!

 

[ohill1981]

Thanks everyone just a follow up .. I have secured the probe and insulated it with bubble wrap.. Chest freezer has my beer at a nice 65F and holding steady.. Thanks to everyone for the info!!!