Furnace blower does not come on.
 

I have a 1988 Trane furnace that has worked fine over the last 3 years. The A/C works fine and the blower works when the thermostat is switched to auto. When I switch the thermostat to heat the gas comes on and the flame ignites but the blower never comes on. I am assuming this is an issue in the furnace. Any thoughts on what might me causing this?

New AC system.

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Bad winding in the blower motor for the heating speed. Could be a bad relay on the furnace control board.