NATE Air Conditioning and Heat Pumps Practice Exam

Which combination of measurements indicates an open heater element?

1. Current draw through the heater elements with no voltage to the heater

2. Voltage to the heater with current draw through the heater elements

3. Voltage to the heater with no current draw through the heater elements

4. Voltage to the heater with resistance measured by an ohmmeter

The correct answer is: Voltage to the heater with no current draw through the heater elements

The scenario where there is voltage to the heater but no current draw through the heater elements suggests that the heater element is open. In a functioning electrical circuit, voltage is necessary to drive current through the heater element. If there's adequate voltage present but current cannot flow, it indicates a break in the circuit—essentially what an open element represents. This condition occurs because the open element creates an incomplete circuit, preventing current from flowing despite the presence of voltage. An effective way to validate this is by performing a continuity test. If the circuit is open, the multimeter will not register any current, reinforcing the diagnosis of an open heater element. In contrast, if current is present without voltage, that condition would suggest an issue with the power supply rather than the heater element itself. Measuring voltage alongside an active current draw would indicate normal operation, confirming functionality rather than a fault. Therefore, identifying voltage with no current confirms that the heater element is indeed open.