Defective t-stat?

[kc261]

I just got 2 new t-stats. They are the johnson controls model A419.

I've noticed a weird thing about them. They both refuse to display 83F as the current temperature. They always jump from 82F to 84F., or from 84F to 82F. Other than that, it seems to go smoothly up & down by 1 degree increments.

Is this normal? Should I be concerned that these units are defective?

[td30]

I just got 2 new t-stats. They are the johnson controls model A419.

I've noticed a weird thing about them. They both refuse to display 83F as the current temperature. They always jump from 82F to 84F., or from 84F to 82F. Other than that, it seems to go smoothly up & down by 1 degree increments.

Is this normal? Should I be concerned that these units are defective?

I have noticed the same behavior from my Johnson thermostats. Do you have it set for 84? Maybe if it was set to 83 it would display 83??? Anyway, I wouldn't sweat it as long as they control fine. Mine do.

[kc261]

I thought the weird behavior might be due to where the setpoint was, so I have tried several things, including 83, and things like 10 degrees higher or lower so it was far away from 83. It still won't display 83F.

Crazy t-stat.

It does seem to function properly otherwise. However, I'm a little concerned that if I can find one defect in it, are there others I can't detect? Is whatever is causing this weird behavior something that could get worse and cause it to fail or have a shorter lifespan than it should? I dunno.

[td30]

Did you buy it from Reptile Basics? Maybe Rich would have some insight for you. I'm sure you could call and ask even if you didn't buy it from him. Personally it is not something I stress about, been running mine that way for months. Let me know if you find anything.

[kc261]

Update on this situation:

First of all, yes I did purchase them from Rich at Reptile Basics. He has been very good, exchanging quite a few emails with me and the problem is resolved to my satisfaction.

Here is a quote from one of his emails (posted with his permission) that might be useful for anyone else that runs in to this problem.

I did some experimenting with a couple of units here and also heard back from Johnson today. They confirmed what my suspicions were. Turns out that it is a mathematics issue with the sensor, not a defect. It boils down to the thermostat thinks in Celsius and it rounds the answer to the nearest whole number in some cases it can not get 83 for an answer. It switches on and off in Celsius even when it is in Fahrenheight mode, it just displays fahrenheight in F mode. Seems that is knows 83 is there but just can't say it. I noticed that when I held the probe on one here it would climb up steadily and sort of pause between 82 and 84 and then keep going. Johnson guy said they most often hear about the stat missing 47 degrees. Apparently that is the other possible black hole. Long story short, it is technically a defect though not really. Seems the unit works fine just doesn't display just fine on some in F mode.

[td30]

Update on this situation:

First of all, yes I did purchase them from Rich at Reptile Basics. He has been very good, exchanging quite a few emails with me and the problem is resolved to my satisfaction.

Here is a quote from one of his emails (posted with his permission) that might be useful for anyone else that runs in to this problem.

Thanks for putting in the time to figure this out. I did not know exactly why it did that only that it didn't seem to affect its function. Thanks again!

[drugaria]

seems like the thermostat is set at a two degree temperature differential. There should be a way to adjust that to a 1 degree.