Set the thermostat to Heat or Cool
Set the temperature above room temperature for heating
Set the temperature below room temperature for cooling
Make sure the thermostat is set to Auto or On for the fan
Turn on the furnace or air handler power switch
Turn on the outdoor unit disconnect switch
Check the circuit breaker for the HVAC system
Replace the thermostat batteries if needed
Make sure the air filter is installed and clean
Wait a few minutes for the system to start
Check that all supply vents are open
Confirm the thermostat display is working
Contact a licensed HVAC technician if the system does not start