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.
On draft: Dry Scrumpy, Smoked Stout, Spices Rum Barrel Aged Coconut Stout,Mutiny IPA
Laagering: New Pils
Up Next: More Spitfire ESB