What troubleshooting step should be taken if the blower motor runs only in the FAN ON position but not in AUTO?

When a blower motor operates only in the FAN ON position but does not run in the AUTO setting, the most logical troubleshooting step is to inspect the thermostat settings. In AUTO mode, the blower motor is designed to operate in conjunction with the heating or cooling system, typically turning on when the system is actively heating or cooling. If the thermostat settings are incorrect or the thermostat itself is malfunctioning, it may not signal the blower motor to operate when needed.

Checking the thermostat can reveal whether it is set to the appropriate mode and temperature settings. It’s important to ensure that the system is calling for heat or cooling and that there are no discrepancies in the temperature settings that might prevent the blower from turning on while in AUTO mode. Also, any issues with the thermostat wiring or a malfunctioning unit could directly affect the blower operation.

While inspecting the refrigerant levels, replacing the blower motor, or testing the capacitor might be relevant in other situations, they are not the primary steps to take when the blower motor runs in one setting but not the other. The thermostat is the key component that manages how and when the blower motor receives power based on the heating or cooling demands of the space.