This relates to a problem I'm having with my gas furnace. I took a power hit and ever since then the blower on my furnace continually runs when I have the thermostate set at off and fan on auto. I repalced the thermostate no help. I did notice the fan runs slightly faster when I switch it from auto to on. I'm thinking it might be the circuit board. Am I on the right track and is there a way to confirm that. It's a carrier natural gas furnace built around 1989. Model 518cxx042000maca. I looked on line for the circuit board and found one for about $70. Part # hh84aa011. What's your advice...