Johnson Digital Temp Controller with Chest Freezer

Got the Holiday 5cu ft chest freezer from Lowe's for my kegs and bombers and I hooked up a Johnson Digital Temp Controller to it.
I originally had the probe just hanging in the air and it seemed like the compressor was turning on too frequently. So I then taped it to the side of a water bottle between a piece of insulation foam hoping to get more of a constant temp of the water in the bottle, but again it seemed to turn on the compressor too much.
Both ways I had it set to 40 with a differential of 5 so that it would stay between 40-45degrees in the freezer, but once it hit 40 it wouldn't take too long before it hit 45 again.
So I took another step and took a gatorade bottle and put a thermowell in the cap and inserted the probe so I could take the core temp of the water in the gatorade bottle.
The probe says it is not waterproof which is why I used the thermowell.
Now I have run into another problem, I have my controller set to "cut out" at 41degrees with a differential of 3. So when it hits 45degrees the compressor turns on and should turn off when it hits 41.
It does turn off when it gets to 41, but the water temp continues to drop and goes down to around 38degrees.
My thought is that it is getting it so cold in there that when the water temp gets to 41 and the compressor turns off, it is still so cold that it makes it drop another 3 degrees. It wouldn't happen when I was measure just the air because it takes less energy for the cooler to drop the air temp then the water temp in the bottle.
From other people's experience, should I just compensate for that 3 degree drop and say set my controller to 43degrees with a differential of 1, so that way it will stay between 40-45 in the chest freezer?
I want to minimize the compressor cycles as much as possible to help prolong the life of the freezer.

I'm not sure what the correct way to do this is but my Johnson digital control has a differential set at 5 and a short cycle set at 2 minutes. My beer temp never goes +/- 1/2 a degree F with this setup and my compressor always runs for at least 2 minutes at a time and with a differential of 5 F it will usually maintain that temp for 30-90 minutes before kicking on again unless it's really warm in the fermenting room.

Jayhem said:

I'm not sure what the correct way to do this is but my Johnson digital control has a differential set at 5 and a short cycle set at 2 minutes. My beer temp never goes +/- 1/2 a degree F with this setup and my compressor always runs for at least 2 minutes at a time and with a differential of 5 F it will usually maintain that temp for 30-90 minutes before kicking on again unless it's really warm in the fermenting room.

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Where is your probe?
I think that is my biggest issue right now. When it was just reading the air temp, the air would warm up faster then the liquids so it would hit the differential point quicker and turn on the compressor.
But, my issue now with reading the liquid temp is that it takes it longer to cool it so the compressor runs longer and when it hits the right temp and shuts off, the freezer is cold to the point where it keeps cooling the liquids another 3 degrees.

i have mine hanging quite low in the freezer, wrapped in bubblewrap.. works quite well, the temp differential towards the bottom doesn't swing very often

HopHead73 said:

Where is your probe?
I think that is my biggest issue right now. When it was just reading the air temp, the air would warm up faster then the liquids so it would hit the differential point quicker and turn on the compressor.
But, my issue now with reading the liquid temp is that it takes it longer to cool it so the compressor runs longer and when it hits the right temp and shuts off, the freezer is cold to the point where it keeps cooling the liquids another 3 degrees.

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Yea if you are measuring liquid temp with the probe you should have a differential set at 1 degree.

Air temp and 5 degree DIF works well for me. I always tape my probe to the bottom of the fermenter such that the metal part of the probe is within 1 inch of the fermenter but NOT touching the fermenter. Works well for me. Maybe you are just opening the freezer too often to check your brew which quickly raises the temp!

Jayhem said:

Yea if you are measuring liquid temp with the probe you should have a differential set at 1 degree.

Air temp and 5 degree DIF works well for me. I always tape my probe to the bottom of the fermenter such that the metal part of the probe is within 1 inch of the fermenter but NOT touching the fermenter. Works well for me. Maybe you are just opening the freezer too often to check your brew which quickly raises the temp!

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Thanks for the help everyone.
I found if I set my cut out point 3 degrees higher then my desired lowest temp and have a differential of 1 it the compressor only runs for a few minutes about 3 times a day.
And I can't put a collar on it for tap handles right now, so I have to keep opening it to dispense off of my picnic taps!