What is the primary purpose of testing the heater and defroster before operating the vehicle?

Testing the heater and defroster before operating the vehicle is primarily to ensure clear visibility through the windows. The defroster is specifically designed to remove condensation and frost from the windshield and other glass surfaces, which is crucial for safe driving. Without clear visibility, the driver may not see hazards or other vehicles, increasing the risk of accidents.

While maintaining a comfortable temperature is indeed beneficial for the driver and passengers, it is not the primary reason for conducting this test. Checking the vehicle's battery performance and preventing engine overheating are important aspects of vehicle maintenance but do not directly relate to the operation of the heater and defroster in the context of pre-trip inspections. The focus is on safety and ensuring that the driver can maintain proper visibility while on the road.