Comfortmaker Furnace won't start, but A/C does. Please Help!
I have two newer (~ two y/o) Comfortmaker furnaces, one for my first floor and the other for my second. The one for the first is working fine, but second floor heat does not go on. I began troubleshooting the faulty second floor furnace by replacing the thermostat, hoping that that would resolve the problem, but that did not work. The non-functioning system's diagnostic code (three long flashes) on the control board indicates "pressure switch is open when should be closed." While on the good system I've got the "heartbeat, or normal operation" - steady quick flashing.
When I power off/on breaker for the bad system the control board has a heartbeat for about a minute, then switches to the three long flashes (when thermostat set to heat). I tested the A/C on the faulty system and it works fine, with control board maintaining a steady, consistent heartbeat.
Additionally, I've powered off both systems at breaker, disconnected wiring from the pressure switches, checked them out with multimeter and both read the same (1), which leads me to believe that the pressure switch on faulty system is good.
I'm confused. Any advice or assistance would be greatly appreciated.
Many thanks in advance,