While troubleshooting a 24-V control circuit consisting of a thermostat, a pressure control, and a contactor coil, the technician reads 24 volts across the thermostat, 0 volts across the pressure control, and 0 volts across the contactor coil. The technician makes the following statements. The following statements are all considered to be true.
A) The transformer is burned out.
B) The thermostat is open.
C) The contactor coil is energized.

Question

While troubleshooting a 24-V control circuit consisting of a thermostat, a pressure control, and a contactor coil, the technician reads 24 volts across the thermostat, 0 volts across the pressure control, and 0 volts across the contactor coil. The technician makes the following statements. The following statements are all considered to be true. 
A) The transformer is burned out. 
B) The thermostat is open. 
C) The contactor coil is energized.

Quizplus · Accepted Answer

The presence of 24 volts across the thermostat indicates it is open (not allowing current to flow), which is consistent with statement B being true. However, statement A is false because if the transformer were burned out, there would be no voltage present anywhere in the circuit. Statement C is also false because if the contactor coil were energized, there would not be 0 volts across it; instead, it would indicate a closed path for current flow.

While Troubleshooting a 24-V Control Circuit Consisting of a Thermostat