EUREKA!
It worked! Thank you a million times!
There are a couple more tweaks needed: The code provides two states. I would need a third one for a long transition from off to the first cool down. The cooler is so well insulated that I may not need it though. It may be able to function well with only short ons, long offs, gradually getting cool enough and able to hold it when off.
The other thing is that there is some on/off behavior between full off and full on. It's so regular, it looks like a blink program. Too many number changes take place on the way to getting inside a window of solidly on or solidly off. I plugged in a three second delay in order to get a good look at the numbers. And I had to change the code settings from 500/520 to 768/762.
The behavior is as follows:
>768: solidly off
<768 and > 762: blink program
<=762: solidly on
I didn't concern myself with actual cooler temps as I'm confident that moving the numbers up and down will take care of that. The fantastic thing is that the program actually works AND, I get to use the thermistors that I had completely given up on! The only problem with them is noise from the power supply I ordered. The testing tonight was with my bench supply that produces no noise. But that's another issue all together.
I'm a happy man if I can get the blinking to go away. Then, all I'll need is some means of killing the noise from my power supply.
Is there some way to put averaging in the program? I'm almost afraid to touch it. But I will though. Gotta try. I'll just keep a copy of this one. Or you can send an updated code if you would be so kind.