I've got a Goodman GMP100-3 that's giving me fits. The induced blower comes on fine, the gas comes on and ignites... but the blower fan doesn't come on. The furnace burns until the limit switch activates, at which point the gas goes off and the fan comes on and blows the slowly cooling air into the house. Once the burn chamber cools enough, the induced blower kicks on again and the cycle repeats until the thermostat temp is reached.

The fan works fine in a/c mode.

The furnace has a new circuit board, limit switch, and flame sensor.