With my temp controller, I had it against the wall at first which funked up the temp readings. Now I sit the probe in a glass of water, so it tracks closer to the actual beer temperature.
I feel like it has nothing to do with the probe and more to do with the actual settings not working. The probe will read whatever temp is in the fridge. Go to the route...why is the fridge pumping at 84 degrees then? Shouldn't it be cooler even if you weren't using the thermostat control? Just throwing some ideas out there. Keep us posted to see if you get it up and running.
"A bad man is a good man's job, while a good man is a bad man's teacher."