I have a 25 year old Carrier furnace. The first problem I had was the burners lighting then after a few seconds turning off, followed by a relight and so on. I changed the pilot/flame detector. The furnace then didn't work at all...not even the draft inducer. I put a screw driver in the fan (outside) and pulled it through like a prop start on an airplane, the motor turned on and the furnace ran again for 24 hours. The draft inducer motor was obviously bad and I changed it out. Now the blower runs constantly, and though the draft inducer has 120 vac going to it, it will not turn on. I tested the motor and its good. I changed out the inducer control board, and did a continuity test on the pressure switch and the limit switch (both good) but no change. Any ideas?