If the air circulation fan inside your house doesn't work when you turn it on (in the "fan on" mode), but the whole AC system works fine when it reaches the set temperature, there could be a few potential reasons for this issue:
Fan Mode Setting: Double-check that the fan mode setting on your thermostat is correctly configured. Make sure it is set to "Fan On" rather than "Auto." In the "Auto" mode, the fan will only run when the cooling or heating system is actively running. If it's already set to "Fan On" and the fan still doesn't work, proceed to the next steps.
Faulty Fan Motor: The problem might be due to a faulty fan motor. Over time, fan motors can wear out or develop issues, leading to a failure in the fan operation. If the fan motor is not functioning correctly, it may need to be repaired or replaced by a professional HVAC technician.
Electrical Issue: Check the electrical connections related to the fan, such as the wiring and circuit breaker. Loose connections or a tripped circuit breaker can prevent the fan from receiving power and operating properly. Ensure that all connections are secure and that the circuit breaker for the fan is not tripped.
Fan Control Board or Relay: The fan control board or relay controls the operation of the fan. If this component is faulty, it can prevent the fan from turning on even when the system is running. A trained HVAC technician can diagnose and replace these components if necessary.
Thermostat Issue: There might be an issue with the thermostat itself. Faulty wiring or a malfunctioning thermostat can prevent the fan from operating correctly. Ensure that the thermostat is properly programmed and functioning as intended. If you suspect a thermostat issue, consider consulting an HVAC professional to inspect and potentially replace the thermostat.
In any case, it is recommended to have a qualified HVAC technician inspect and diagnose the specific problem with your fan. They will be able to identify the exact cause and provide the necessary repairs or replacements to restore proper fan operation.