Originally Posted by McKBrew
If you can't adjust the temperature swing by more than 1 degree, you might be cycling the freezer a bit much. Most temp controllers have increments of up to 10 degrees allowing more change in ambient temperature before the power kicks back in.
To follow up on this, the problem is that air temp swings wildly, and the probe will pick up on that.
To solve that issue, you want to build in a thermal buffer, something with a lot more thermal mass than your probe so that the wild swings aren't constantly cycling your fridge.
Easiest way to do this is to immerse the probe in some liquid. Fill a pop bottle with water, punch a hole in the cap, and stick your probe through the cap and into the water. Voila...now your probe will take a lot longer to respond, (as the water will take a while to heat up and cool down), and your fridge wont' cycle as much, BUT will still hold the same temperature on average....and you are worried about the temp of your beer anyway, right?
If your probe isn't waterproof, a quick dip in some hotglue/wax, or plasti-dip, should do nicely.