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New Chest Freezer

After months of procrastination, I finally got myself a chest freezer - planning on brewing Oktoberfest today so I plugged the freezer in to my Temp controller and set it to 55F.
But when I passed it 15 mins later, I noticed that while the freezer is definately turned off ok, the sensor is reading 45F. I guess the freezer will continue to cool even after it has been turned off.

Any recommendations about a way to fix this - I guess for my immediate purpose, I can set to 58 so that fermentation will still be in range but I’m worried about the long run - if I have kegs in there at 38 or so, and maybe they go down below freezing?

Thanks for an ideas

Are you sure you have your temp controller set correctly? You might have the offset too high. On my controller, you set the temp to a level that the freezer will cool, but then you have to also set the offset. For example, if you had the controller set to 55 with an offset of 10,the freezer would turn on at 55 or above, and then cool it down to 45 and turn off.

Otherwise, is your sensor location changed from original location? If it is now resting on the bottom any was originally suspended in air, that will also give you a colder reading.

The sensor is reading the air temperature inside the freezer. The temperature controller will shut off the freezer when it drops below setpoint and the air temperature may continue to dip for a little bit. I wouldn’t worry–the temperature of the 5 gallons of wort won’t change anywhere near as fast as the air temperature. The air temperature will warm back up and stabilize shortly after the freezer shuts off. Try taping the sensor to the side of the carboy/pail, covered with some Styrofoam or insulation. That will give you a much better indication of the wort temperature.

So wait, there were two posts in a row here. One said the freezer activates at the set point, and shuts down at the set point minus offset. The other says that the freezer shuts down at set point implying it comes on at set point plus offset. (which seems more correct to me.)

I have a self-programmed controller, so I’m not the best source for info on the commercial offerings. With mine, I have a target set point, currently 64. The freezer then has cut-in and cut-out thresholds currently set to 1.4 and 0.7 respectively. This means my freezer turns on at 65.4 and runs until the temp <= 64.7. The fact that there is cold refrigerant in the walls keep the temperature dropping for another few minutes. It will get to about 63.7 before it settles and starts rising again. I try to keep it tuned so that the carry-over cooling doesn’t cause the heater to come on, and vice versa.

I thought most of the two-stage controllers had similar settings…

I would think it would depend on which controller the OP has and how its set up. With my Johnson controller, I can use the setpoint as either the cut-in or the cut-out value. That said, I notice that my freezer has a bit of “thermal inertia”, in that it usually continues to cool down a bit (maybe a degree or two) after it reaches the cut-out point, and it sometimes rises a degree above the cut-in point.

Thanks for the replies - I must say I wish I’d stayed in school longer when it comes to setpoints and differentials.

I was messing with it today though (Its the Johnson contoller from this site - and I had removed the jumper to put it in cool mode) and it sems that I was my own worst enemy - in trying to trigger the on function, I was holding the sensor in my hand which was throwing the temperature up above 60 in an instant - as a result the freezer had to work longer to get it down to 55 so I can see know why it would continue to cool a bit longer.

But when I let it just cointrol itself, it seemed to regulate better - I did end up changing to 1 minute whatever it was called that was stopping it from cycling too quickly - and also taped the sensor to the carboy like suggested.

All in all, seems to have turned out ok, Thanks for the replies and its good to be back brewing after a long winter :cheers:

I would bump that back up to 5-10. It’s my understanding that fast cycling is really bad on the compressor. In normal use it will not be an issue. Generally mine needs to run the freezer for 5-10 min, then it sits idle for a longer time than that threshold. When a fresh brew is actively producing heat it may run every 45 minutes or so, after the yeast has settled-down it may only run 2-3 times per day.

Unless I’ve been opening the lid and/or messing with the probe position, I don’t really think I’ve ever seen short-cycle protection kick in.

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