You need to very carefully make certain the blower motor wires are connected correctly to the control board. If this is a PSC motor then you should have at least 3 speeds and 3 corresponding wires from the motor in addition to the common from the motor. Usually high speed motor wire connects to the AC plug on the control board and the low or medium speed to the Heat plug on the control board.
If that connections look good, remove the Heat motor wire from the control board and with the furnace on. measure the AV volts between the Heat terminal on the control board and the common (or use the furnace chassis frame). You should get 120 volts AC. If you show 0 volts then check the board for cold/loose solder joints. If all joints are ok then the relay may be bad.
If you get 120 volts AC at the control board then try the unused motor wire... it should be taped. If that doesn't work, I would closely inspect the motor itself.
Problems related to residential installations.
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