I have a 12 year old Trane A/C and Gas heat air handler> It has run great up until three days ago. I didn't notice until theweather cooled off here in AZ. When I trun the thermostat up to heat the house it click like it is going to work. It won't even turn on. I have checked the power to it and it runs off the same power as its sister unit (upstairs & downstairs) I have switched the thermostats thinking one went bad. The fuse (5 amp) inside the air handler is fine, but it won't even click on if I try to run the A/C or just tunr on the blower using the "On" vs the "Auto" switch. Any ideas before the HVAC guy shows up and charges me for the first born?

Might be the start capacitor on the motor or a bad motor. Open the fan housing, depress the safety interlock if equipped ans try to run the unit. If it tries to run but barely turns, it is most likely the capacitor.Look for a round or oval shaped can on the motor, ground the leads and then remove the capacitor. Take it to an electrical supply store and get as close a match as possible. Replace it and hopefully it will start. If nothing happens, make sure you are getting power to the motor. If so and nothing happens, it's probably the motor. If you are lucky, only first born will be required. Figure 300-500 depending on the motor.