I have a York Furnace in my attic (model: p2mpd20n08001c) that sheared its blower motor shaft when the blower fan slipped off and it kept running.
I got my hands on a new 1hp blower motor that included a fan, control board, capacitor and wiring. The old one was a 3/4 hp motor. Since there was a change in amps (12.1 vs the old 11.0), I decided to use all the new parts and just hook up all the above to the old unit's wiring.
I got that completed Monday evening, and we had nice, cool air blowing again after a weekend of heat. We had some storms come through and our electricity was blinking on and off a few times each day, and Wednesday the blower fan stopped working again.
I replaced the transformer when I incorrectly diagnosed it as the faulty part before realizing that the circuit board had blown. When I pulled the control board out there was a black mark on the back, and a corresponding black mark where it was mounted.
I got a new circuit board this afternoon and hooked it up. The fan ran for 2 seconds, then I saw a flash and heard a pop, and it stopped. The new circuit board blew in the same place.
I called a HVAC guy who told me to just hook up the black fan wire to the L1 lead from the outlet and take the circuit board out of the loop and I'd have A/C, but my blower would run all weekend while I waited for a new circuit board on Monday.
When I do this, it runs for a second or two, then trips the circuit breaker and stops. I figured the water collecting in the drip pan was to blame, so I removed all the water from the pan and inside the blower fan case, but it still shorts out.
My best guess is the water leaking from above has collected inside the motor and is shorting it out, since there's no other reason it should short. The green wire is grounded, the white is still on the circuit board on the common line, and the black is connected directly to the hot black coming from the outlet.