Ok. So I found the specs on my fan switch. It's a 110*F fan switch:
OEM Coleman Evcon Furnace 110 F110-20F Disc Fan Switch 7660-328 7660-3281 4066-3281 - North America Distribution-Sellersburg Heating
I tested it in a plastic bag in water. It seems to come on and off right around 110F.
I went ahead and ordered an adjustable one with a lower limit of 70*F/90*F off/on to a high limit of 110*F/130*F off/on. I'll let you know how it goes.