Hi. I have a Rheem Classic 90 Plus Series Contour Furnace and the blower motor will not run. The A/C will turn on, and I can hear the gas ignite, but no fan or blower motor. Removed the cover and the display on the circuit board flashes 81, 68, 81, 68 then solid F for about 4 seconds then continues flashing just 81 over and over. The back panel lists code "68" under "ICM Feed-back signal" and supposedly means "no signal". Code 81 is listed under "thermistors" and means "return air sensor - out of range. "F" means "System Fan - no heat or cool cycle - fan on"... which is correct because I have the HRV on, which automatically turns on the fan for the furnace.

Any idea what I am dealing with here? Any guidance would be very much appreciated.