By air flow control swotch, are you perchance refering to the speed control for the blower? If so, you probably have a burned out speed control resistor. The blower speed is controlled by inserting resistance in series with the motor. The speed control shorts out parts of the resistor progressively in steps and at maximum speed, the entire resistor is shorted (bypassed). By your description, the motor is good, there is electric power avalable to the heater motor circuit, therefore, fuses/breakers in the circuit are good. You'll need to consult a repair manual to locate the resistor assembly. Often, these are mounted on the air flow duct with the resistors in the air flow. The resistors are cooled by the induced air flow. If you are lucky, it is accessible from under the hood, but if unlucky, it'll be under the dash.

You state the original motor overheated when the insulation fell on the housing. Are you sure about this? I would think the motor would no longer operate if the internal mechanism became so hot to give off a strong smell. Are you sure the new motor is overheating? Does it feel very hot when you touch the housing? You stated you have changed the motor from a 1/3 HP to 1/2 HP. Have you set the air flow so that it is the same as the 1/3 HP motor? The smell may be coming from something unrelated to the motor. If the smell is giving you a headache then you should have a professional inspect the heat exchanger. You may have a more seious problem.

I checked and replaced the filter. But now if I turn on the air conditioner and then turn it off, the outside unit continues running, it should not be. (Is this a contactor problem?) Thank you very much for your help. Yes it 'could' be a contactor problem, but it could also be some other problem that causes this action. You've already guessed a few times and are no closer to fixing this. It may be something as simple as replacing a contactor. But this part is an important part that controls your AC. It would be better to call a licensed HVAC contractor to solve this problem and possibly identify another problem with the upstairs zone control. Zone controls are more complex, really not intended to be home owner serviced. It sounds to me like you have more than 1 problem with your zoned AC system. I service the Katy, Texas area.

Park is usually a dead plug where the wire is put to keep it safe from shorting out against anything. You probably need a new motor. The PCB seems to work fine. If the motor does not growl while operating, the motor is probably bad. If it growls, replace the cap first. As to the techs out there- This is the beginning of my new standards for this site. I will help as much as possible to anyone that seems capable. I will try not to insult the poster. A motor replacement is a good test of skills. You need a few tools, and just a little experience with electricity. Like how to switch off the breaker or switch. I am tired of hearing that someone paid $500 for a new $50 motor. Always replace the cap. No excuses, replac3e the cap with a new motor. Do not pass go, until you replace the cap. Otherwise go to jail for your stupidity.