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

In an electronically controlled automatic temperature control (EATC) system, the ambient temperature sensor is typically a thermistor. The behavior of most thermistors, particularly Negative Temperature Coefficient (NTC) thermistors, is that their resistance decreases as temperature increases. Therefore, if the ambient temperature sensor is exhibiting increased resistance as it is heated, this behavior suggests a malfunction or incorrect operation of the sensor.

Since the question indicates that the sensor shows increased resistance when heated, this aligns with a scenario where a technician is correctly diagnosing a faulty sensor or incorrect wiring, as it deviates from the expected operational characteristics of a functioning NTC thermistor.

Technician B’s assertion regarding the increased resistance in the context of a malfunction is accurate, justifying their position. In contrast, another technician might have provided an explanation that does not align with the expected behavior of the sensor. Thus, focusing on the definition and function of the ambient temperature sensor is key to understanding why Technician B’s reasoning is correct.