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Does the blower work in AC mode and just not in heating mode? Does the blower run when you set the thermostat in the FAN ON mode?
If you can attach a close up photo of the wiring diagram glued inside the blower service door, well lit, taken from straight on and well focused, and a picture of the printed circuit card in that area that shows the thermostat wire connections, I can mark those up with trouble shooting directions.
You can use the paper clip icon at the top right of the tool bar for that.
We can go from there.
So far it sounds like a bad printed circuit card. or the fan motor would run in either heating or cooling mode at least.... 80% chance its a bad printed circuit card, about a 20 chance its a bad fan motor or bad fan motor run capacitor.
You can test that with a clamp around amp meter, put it around one wire at a time that runs to the fan motor, tell me what the reads are. Do it with system in cooling mode set to 55F to insure that the fan should run..
You can buy a clamp around amp meter at Harbor freight for $25 or for $50 at any large hardware department such as Home Depot or lowes.
Let me know what you discover, we can go from there.
That will work. I will be here until 10 pm tonite then back all day tomorrow.