More freezer questions

OK, looking for experience i queses. i have a new 7.2 freezer (SWMBO said i would be happier with a new one so who am i to argue) and Brewers Edge controller II. i have the set point at 40 and the differential at 1 deg. as i understand it, the unit should turn on at anything above 41 and turn off at anything lower than 39. right?? the turning off thing is working perfectly but the temp runs down to 35 or 36 on the low end. i have not sat on the freezer and watched it turn off because the cycle takes a couple of hours and i have other things to do. if the unit IS shutting off at 38, does the freezer keep cooling from the charge that's in the line? i have the probe immersed in a wine bottle with water in so i can get a liquid temp and not an air temp. my other question is that i placed a digital thermometer on the bottom of the freezer to check some "zone" temps and when the controller probe reads 36 the therm at the bottom is at 29. im worried about freezing. anybody have any experience with this stuff. i would greatly appreciate some guidance.

thanks

There will always be a temperature gradient in the freezer from top to bottom unless you install a fan to circulate the air. Putting the probe in a container of water causes the controller to lag considerably. What happens is that the compressor will turn off when the temp drops to the set point minus the differential. The way you have it set up, the compressor will turn on at 40 and shut off at 39.9 with the 1 degree differential. The problem is that the freezer evaporator (chilling ) coils are in the walls of the freezer. The walls get very cold and stay that way for some time after the compressor turns off. The temp will continue to drop for awhile and undershoot your target temp. The reverse happens as the freezer warms. The water bottle with the probe will not warm up very quickly and as a result you will overshoot the target temp before the compressor turns on. Warm air rises and the temp near the top of the freezer where the beer lines and taps are located will likely be warmer than you want. This can cause foaming problems and the beer won't be very cold initially out of the tap. So, you might think that turning down the controller temp might help, but that can sometimes result in the bottom of the kegs freezing. The bottom is where the beer out dip tube is located. If it gets blocked by even a small amount of ice, you won't get any beer out of the tap at all. I've been through all this, so I'm speaking from experience. My solution was to install a muffin fan inside the freezer to circulate the air and I have the temp probe near the top of the kegs. I usually have the controller set to 40 F with a 5 degree differential, so the air temp drops to 34.9 very briefly and then slowly rises to 40. I've arrived at these settings through trial and error. You may prefer different settings depending on how cold you want to serve your beer. You can get a good idea of how well everything is working by measuring the actual temperature of a poured beer. It's nice to have the first beer pour at the same temp as the subsequent ones.

+1 on installing a fan. I have a small computer fan (120v) that runs constantly.

thanks for the replies. i am actually using the freezer for lagering and cold crashing. i haven't graduated to kegs yet. i figured the water in the wine bottle would mimic the wort/beer liquid temperature better than testing the ambient air inside the freezer. the fan is great idea though. i will be implementing that tomorrow.

What I do for lagering - is leave the probe in the air - and put a stick-on thermometer on the carboy. My temperature controller has a 2 degree differential. If I set it at 40F - it turns on until 40F is reached, then off until the temp is 42F.

The air temperature does cycle to below 40F after turn off, but the volume of liquid is great enough that its temperature does not vary and stays at 40F, as evidenced by the stick on thermometer on the glass carboy.