Johnson Analog differential, which way does it go?

Hi All,

Question. i have searched and have seen 2 different answers to this question.

I understand that the Johnson analog controller has a fixed differential of 3.5F = 2C, so lets just say it is 4F.

Assuming I have the set point @ 65, does it -->

A. Cool to 65, then when it raises to 69, kick in and cool to 65 = avg 67
or
B. Cool to 61, then when it raises to 65, kick in and cool to 61 = avg 63

I have seen it stated both ways, on this board and others. The docs do not state it clearly either.

Right now I have it set 62, and when I check the temp, it is usually around 66 or less. So I am going with A.

BTW I have it hanging inside the freezer measuring the ambient air temp.

Thanks in advance

Paul

I'm was told by my LHBS that it is below the set point, but I dont have a thermometer in the keezer so I'm not sure. I think it depends on how it is wired inside. I'm trying to wire another one(given to me)that came without a cord and inside it looks like depending on how its wired it can open either way.

I just started using the Johnson analog controller...and I'm not thrilled with it yet. The way I understand it...your set temp is the high end of the 4 degree swing. If your set temp is 66 then the unit should come on and cool to 62. However, i've checked on it a few times and the temp inside my chest freezer was 70. It's obviously not kicking on when it should. If anyone using this controller has any advice i'd love to hear it.

Mine seems to work the way it's supposed to. The only time I've ever seen the fridge thermometer higher than the johnson setting was when I kept the fridge door open too long and the cold air dumped out.

I put mine in a test tube filled with the gel from a ice pack. seems to work okay. I have a digital ranco for ferm and the johnson for the keezer, so i'm not to worried about a temp swing. the gel seems to work though, and the probe doesn't look like it's rusting or anything. I didn't want to put water in the test tube because you'd have to refill it every once and a while and I wasn't sure what it would do to the probe.

I am not sure it really matters. The temperature markings on my controller don't really match the temperature in the fridge, so I just use a max/min thermometer to record the range of temps I am getting. If the range is too cold or too hot, I adjust the temperature controller accordingly (and I don't even pay attention to the markings on the dial anymore).

I believe that "A" is your answer. That's been my experience.

Thanks for the responses all!

Flyguy, that sounds like a great idea. I think I am going to have to try that with the min/max thermometer. I have already noticed that the controller analog dial is somewhat off from the internal temp, so once I have nailed down the differential, I'll know what to set at.

Thanks

Paulbill