Did this just start happening? Does the fan work in the on position on Hi or Low speed? Could be a faulty circuit breaker in the panel or bad t-stat. Unplug the coach and remove the breaker and check it for contunuity. If good then remove the filter access panel and filter, check the molex plug to be sure it is 100% mated. If so take a multi-tester and OHM out the t-stat wires to be sure there's no break in the wires between the AC and the t-stat. If everything checks out from a wiring standpoint it most likely is the t-stat. I'd swap out the front t-stat and the rear and see if it works then. Be sure to turn the front AC breaker off before doing this.