Heating, Ventilation, and Air Conditioning (HVAC ) Electrical Practice Test

When the voltmeter shows no measurable voltage on L1 and T1 terminals of a contactor, what does this indicate?

1. Bad contactor coils

2. Good clean contacts

3. A power supply failure

4. An overload condition

The correct answer is: Good clean contacts

When a voltmeter shows no measurable voltage on L1 and T1 terminals of a contactor, it typically indicates a power supply failure. The absence of voltage suggests that the circuit supplying power to the contactor is not functioning properly. Contactors require a specific voltage to energize their coils; if there is no voltage, the contactor cannot operate, leading to the conclusion that there may be an issue upstream in the power supply. Understanding this, the presence of voltage on these terminals is critical for the contactor to engage and maintain the electrical operation of connected devices. If the voltmeter indicates zero volts, this often directs technicians to investigate potential sources of power loss, such as a tripped circuit breaker, blown fuse, or wiring issues. In operational terms, clean contacts would imply that even without power, there are no signs of arcing, burning, or corrosion, which means the contactor itself is likely still in good shape operationally, but the lack of voltage clearly points towards an issue with power supply. The other choices—bad contactor coils, an overload condition—would not typically result in a complete absence of voltage at the contactor terminals; these issues would manifest differently, often keeping voltage present but potentially causing the contactor not