Upon arriving at the site, I first diagnosed the issue with the heating unit, which had tripped out on the main limit switch. This is a safety mechanism that shuts down the unit when it overheats. I increased the blower fan speed to ensure proper airflow and prevent overheating. Additionally, I replaced the old air filter with a new one to enhance the system's efficiency and improve air quality. After these adjustments, I tested the unit to confirm that it was operating correctly and safely.