Temp Control troubleshooting help

[Baloo]

Hi guys,

I'm in the process of converting a chest freezer (about 14 cu. feet) into a keezer. I bought a Johnson Controls analog controller, plugged that bad boy in, and set it to 35 degrees. Right now, in a fairly stable environment (between 35-50 degrees ambient), the temp in the freezer fluctuates between 36 and 42 degrees. Is this normal? I (possibly ignorantly) assumed that the controller would keep the temp within a 2-3 degree window. Anyone have any ideas?

Much Thanks,
Baloo (Bryan)

[noremorse1]

Is there anything inside the freezer? I believe the Johnson analog will cool to 3 1/2 degrees below what you set the temperature at and then shut off until it rises above what it was set at. If the freezer is empty, there is no thermal mass. a Freezer that big will struggle to maintain that temp empty. Also, where do you have the probe mounted? this will influence the management of the temperature as well.

[Baloo]

I currently have 5 gallons of ipa conditioning in there, as well as a couple sixpacks. Short answer, not much, and you may be on to something. I was given a tip from the LHBS to stick my probe into a body of water inside the freezer, so I have it inside a nalgene of water in the bottom of the unit.

[noremorse1]

Someone just posted on the homebrew talk forum saying he has his set at 35 and sees temps between 38 and 43 with the same controller as you. So I guess this is normal.

He even graphed it :
http://www.homebrewtalk.com/f11/johnson ... ile-88329/

[fermentalist]

Had a similar unit once upon a time with probe in wine bottle in chest freezer. That IIRC had independently adjustable differential and temp setting, but at tightest differential, kept the wine bottle +/- 2 degrees. Course a slowly fermenting or inactive carboy likely experienced a much smaller swing. I'd say you're good to go. Duty cycle was pretty reasonable at 40 F, trying to keep within too narrow causes too much cycling wear/tear.

[Mylo]

I think the consensus is that the analog johnson controls are fine for serving - but their temp thresholds are to wide for controlling fermentation. I use a digital Ranco's with a 2 degree differential (to avoid over-cycling the compressor), connected to the freezer for serving. Because my ferm temp control is actually managed by fans - I set that for a 1 degree differential.


Mylo

[Baloo]

Sounds good, thanks guys!

Baloo

[bub]

I use a brewdroid prototype... it is nice
BUB