How to force a blower motor to work?

Forcing a residential indoor air handler blower motor to work for diagnostic testing requires bypassing the thermostat and control board relays by applying direct power safely. First, turn off all electrical power to the air handler at your home's main circuit breaker panel for safety. Second, remove the service access panel to expose the blower motor wiring compartment. Third, consult the wiring schematic on the unit door to identify the high-voltage line power wires and the specific speed wire (such as high speed). Fourth, using extreme caution and insulated tools, you can temporarily apply 120V line power directly to the motor's common and high-speed leads while ensuring the motor is properly grounded. You can verify that this procedure is successful when applying direct power causes the blower motor to spin up immediately, indicating that the motor itself is healthy while the control board or thermostat is at fault.