Cool, another electronics geek!
It appears that the hysteresis loop is wrong.
When the output of the the comparator goes high, the hysteresis circuit tries to raise the setpoint voltage, which would turn the comparator off. When the comparator is off, it tries to lower the setpoint voltage, which would turn the comparator back on.
In short, this is not wired as hysteresis - it's wired as an oscillator! And it would be oscillating like crazy if it were not for the fact that the setpoint voltage regulator is connected to the comparator's negative input *without* a resistor - meaning the LM317 is actively cancelling the effects of your erroneous hysteresis circuit.
Hysteresis should be on the positive side of the op-amp. Connect LM411 pin 6 to LM339 pin 3 with a resistor. Connect LM339 output to to LM339 pin 3 with a fixed resistor and variable resistor in series. That's a proper hysteresis circuit. The actual hysteresis is determined by the ratio between the resistance of the hysteresis circuit and the resistor on the input from the previous op-amp.
This is a good page to see how hysteresis works.
The relay driver could use some cleanup too, but that's not a functional change.