Our furnace quit working Saturday morning. I noticed it around noon after being out all morning. Our thermostat automatically lowers the set temperature when we are away but when I bumped it up, nothing happened. I called our Heating and Cooling company for some emergency service but nothing was available until Monday. Having spent 40 years in various maintenance fields, I decided to troubleshoot the problem and see if I could get it running. It was 30F out and Monday was a long way off. I got out my multimeter, opened up the furnace, and checked everything. I found that I had power to the induction motor but the motor wasn’t running. Ahah! Bad motor, problem solved. This also matched the fault code flashing on my circuit board for a pressure switch not being made. I looked up the part and took off for the parts store 40 minutes away.
90 minutes later, I arrived back home with my new part in hand. Another 30 minutes and the part was installed and I was ready to give it a test run. I turned power back on and waited for the thermostat to come back online. It called for heat, the motor turned, and nothing else happened. Several attempts and still nothing. I decided to wait for the professionals now. I wasn’t sure if I had a cracked plenum or not since this could also cause the pressure switch not to make. That would have been dangerous.
Monday afternoon the Heating and Cooling tech arrived. He did some preliminary troubleshooting and ended up at the same place I had arrived at. He was sure the furnace was going to fire up and thought maybe the thermostat was bad. He bypassed the thermostat and still nothing happened. As it turned out, the circuit board was bad along with the induction motor. While this wasn’t an inexpensive repair, it was still cheaper than a new furnace would cost.