Automotive Service Excellence (ASE) Air Conditioner Certification Practice Exam 2025 - Free ASE Air Conditioner Practice Questions and Study Guide

The scenario where a blower motor only operates on high speed typically indicates a failure in the blower resistor. The blower resistor controls and regulates the voltage supplied to the blower motor, allowing it to operate at various speeds. When the resistor malfunctions, it usually leads to failure in all but the highest speed setting. In most vehicles, the high-speed setting bypasses the resistor, drawing full voltage directly from the battery, which is why the blower motor operates only when set to high.

In contrast, issues like a defective blower relay or a faulty blower switch would likely prevent the motor from working altogether or affect multiple speed settings. A blown fuse or tripped circuit breaker would also inhibit any operation of the blower motor, not just limit it to high speed. Therefore, a malfunctioning blower resistor is the most logical cause when the blower motor functions solely in its highest capacity.