I've been working on a Whirlpool furnace that's about 30 years old. I replaced the blower motor because it locked up. Upon putting the new motor in it performed wonderfully while I was on the premises. I throughly checked out all the functions before I left and it was doing great.

The next day I had to return to my customer because the motor wasn't working causing the condensor to freeze up. After investigation, I discovered that the fan motor would run for about 2 minutes and stop. I checked everything from the motor to the relay to the thermostat and back again and concluded that the voltage at the motor wires would read 120v even when the motor would quit running.

One more necessary detail... The old motor had the specs engraved on it and everything on the new motor matched except the horsepower. The old motor had 1/2 HP and the new one was 1 HP (everyting else was the same). Wondering if this could possibly be an issue I decided to change the speed of the motor from HIGH to MED/HIGH. When I did the motor ran for 10 minutes without stopping. I let it run another 20 minutes, checked airflow,etc. and Elvis left the building thinking all was well.

Would you believe they called me today and said the unit froze up and the fan wasn't running. Please help! I'm flabergasted and have to go back tomorrow and try to get my $200 motor working. All the unit has is....
1. Blower motor
2. fan relay (working fine because its an old style that you can see the guts of)
3. Limit/timer
4. Remember the 120v is present at the motor even when it shuts down.