1. Resistor: Make sure you replaced the control resistor correctly and that the new resistor is compatible with your Grand Am.
2. Wiring: Check the wiring going to the control resistor and the heater fan motor to make sure there are no loose or damaged connections.
3. Fan motor: The heater fan motor itself could be the problem. Check for power at the fan motor and make sure the motor is not seized or damaged.
4. Climate control module: The climate control module is responsible for controlling the heater fan speed. Check the module for loose or damaged connections, and make sure the module is receiving power.