During that day, it slowly became apparent that the A/C is not working. I live in a single family house and we have a relatively modern Tempstar A/C. Here's what is known to be working: the outside condenser/fan unit is running fine. The thermostat on the 1st floor is fine and sends 27 VAC downstairs.
The circuit board APPEARS to be okay as it sends 127 volts down to the speed control box, which in turn is connected to the motor. There is nothing obviously burned on the control board, and the fuse there is fine also. (central circuit breakers are also fine obviously).
As far as I understand, the speed control box has capacitors that start the motor. The motor is connected to the box with a green ground wire and red, yellow and blue wires. If any combination of these wires is powered briefly by 127 volts, as I tried, the motor vibrates but does not turn. There is no capacitor box on the motor, so I concluded that the capacitors in the speed control box are for starting the motor.
There is also a separate bunch of small wires going from the board to the control box. It is possible that they somehow erroneously tell the speed control box not to start the motor. Hard to say. So far I see two possibilities.
1. The speed control box is fried.
2. Somehow the board is damaged and even though it sends 127 volts to the inputs of the speed control box, it incorrectly tells the box via small wires to not start the motor.
The speed control box is easy to replace.
What should I do here? Try to find a replacement speed control box?
We called a bunch of A/C places, they said they'd call us back, but no one did. So I figured I can as well try to do it myself.