Furnace Fan Control Mystery- Solved
When we first moved into our house, one of the first upgrades we tried was to replace the HVAC thermostat with a nifty Nest unit. We thought it was working fine until we got the energy bill for that first month (over $300). Our Trane XL80 two-stage furnace seemed to be doing a good job keeping the house warm, yet appeared to be working too hard to accomplish that (it would be on for long stretches of time). That's when I started to pay close attention to how the furnace was behaving. Whenever it started I would head to the garage and just watch and listen to the unit operate. I would head back into the house and stand under the intake and listen. It didn't take long to learn that the unit was shutting off and restarting multiple times even before reaching the temperature set point. But why? Why was it taking so many breaks? I removed the front panel of the furnace to reveal its insides: In the top left corner exists the White-Rodgers Model 50A51-495 control board. On it there...