In a pre-trip inspection, what is the first step when checking the heater and defroster?

In a pre-trip inspection, the first step for checking the heater and defroster is to move the switch from heat to defrost. This action allows the driver to test the defrost function, which is crucial for visibility during driving. By engaging this setting, you can determine whether the defrosting components are operational and effectively clearing the windshield of moisture or frost.

This initial step is essential because proper defrosting is vital for safety, ensuring that the driver has a clear view of the road. If the defroster is not functioning correctly, it can lead to dangerous driving conditions.

The other options, while important in the overall assessment of the heating and defrosting system, come after confirming that the defrost function is working. Checking coolant levels, inspecting the blower motor, and looking for air leaks are all necessary maintenance tasks but are secondary to initially ensuring that the defrost is operational. This prioritization helps ensure that safety mechanisms are functioning first before conducting a deeper analysis of the system's overall health.