Heater and AC not working unless it's on the highest level what do I do?

If your heater and AC only work on the highest setting, it may indicate a problem with the blower motor or a faulty resistor. First, check the air filter to ensure it’s clean, as a clogged filter can restrict airflow. If the filter is fine, consider inspecting the blower motor and resistor for any signs of damage or wear. If you're unsure, it’s best to contact a professional HVAC technician for a thorough diagnosis and repair.