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You must physically follow the wire from the thermostat to where it connects, then follow those connections back until you find the point where the power is broken, in a car wash it is likely to be a badly corroded wire nut or wire terminal connection... when you see such corrosion you are on target to find the problem.
If you rate my advice so far positively, I can hold the question open for ongoing coaching as needed.
Hello again, I see none of our other experts have picked up your question. It is a long shot if you will find anyone here, or even locally that has worked on that particular problem with that particular system,
However I have been in this business for 51 years so far and only very rarely do I find something that I am unable to sort out, with brand names, and model numbers I can get most of any systems wiring diagrams... let me know if you would like to continue on that basis or if I should stay opted out.
We can go from there if you wish.