Temp control acting different on carboy

All,

The last beer that I did I used a bucket for my primary. The temp probe from a Johnson controller was taped to it and the temperatures were great (within 2 degrees).

I'm using a better bottle for a primary this time, and the temps are wildly fluctuating. The controller is set to 66 with differential of 2. The last I checked, the temp was showing 58 degrees. The probe is taped to the side of the better bottle and I have a single piece of bubble wrap taped over it. Is there a better way to do this for a better bottle? I'm afraid that the temps my get too cold for the ale yeast that I'm using and this is a chest freezer.

I use Syran wrap to attach the probe to the side of the carboy and I go around a few times.

Is it switching properly? What happens when the temp hits 64? Does it turn off and then just keep dropping anyway?

Yeah, it turns on and off. I looked at it this morning and it was at 64 which would be correct. Currently, it's sitting at 65. It seems like it's stable enough now. The yeast hasn't started yet, so I'm concerned that it really did hit low temps at one point.

58 is not bad for yeast. It'll be fine.