Ive working on installing a Lincoln town car electric fan with a thermal switch to cycle it. For now I'm installing the thermal sensor in the thermostat outlet.
So I think I have a bad sensor no matter how warm or cold I set the controller it won't cycle the fan have a backup and the read totally different resistance
Got another fan controller from autozone not to impressed with it. Seemed to work ok last night then failed to turn the fan on this afternoon even when turning the AC compressor on.
If you're going with that line of thinking, see if coil of the existing relay is energized when you think the fan should be on. If not, determine if power or ground is missing. If the coil is energizing, see if the N.O. terminal has power at the same time.
Wiring,fuses and relay checked everything looks good. After sitting overnight the fan controller works as advertised. Can a relay get hot and temporarily fail? I have a spare if it does I plan on driving the car around town to see if I can replicate the problem.
Relays can fail with heat, but a 75A Bosch should be fine. If you were running a 30/40 SPDT/SPST before, that might not have been able to handle the steady-state load, let alone a start-up after steady state.