Hey guys, I have a furnace with a Honeywell ST9120C-4040 System board in it.
My heater works fine but my A/C won't kick on (worked fine last year) anyway I'm a complete noob at this HVAC stuff, but I pulled out my meter and the signal from the transformer is 24V.. the diagram on the Carrier AC unit says "External Power Source 24V"... but the signal going over the 2 wires out there is only 5V (When the T-Stat is set to AC on)... So is it just that I need to replace this board? Or is it maybe something on the carrier not sending a signal back?
Maybe it's that simple and it's just a dumb question but figured I would ask before dropping the $105 on the board.
Thanks in advance