I've bread-boarded and bench-tested this one. It will do the essentials as long as your pump and pelt are activate by relays.
At a cold side temperature above that set by the 50k pot, the lower comparator has a zero volt output, which keeps the optocoupler off, which keeps the motherboard from getting the power-ok signal. After a little thermistor chilling, the comparator goes high, turns on the opto, and the board boots. With the comparator high, the 150k resistor provides positive feedback, putting the reset temperature about 5 C higher.
On the hot side, a similar thing. If the temperature is too high, the upper comparator goes low, turning off the optocoupler and interrupting the powersupply-on line, which shuts off PSU.
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I think the hardest thing to do is get the temp sensor interfaced, why not work on that?
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OK. What've ya got?