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

If the blower motor runs when the fan switch is moved to the FAN ON position, what could be the cause?

1. A power supply issue

2. A faulty compressor

3. A faulty thermostat - AUTO/FAN ON switch

4. A blown fuse

The correct answer is: A faulty thermostat - AUTO/FAN ON switch

The correct answer highlights a situation where the blower motor operates in response to the fan switch being set to the FAN ON position. This scenario indicates that the control mechanisms linked to the thermostat and its settings are functioning as intended. In this case, the thermostat's AUTO/FAN ON switch is correctly allowing the blower to run continuously, suggesting it is operational. When considering the functionality of the HVAC system, if the fan switch is in the FAN ON position, the blower motor should indeed run. This position is designed to have the blower fan circulate air regardless of whether the heating or cooling system is actively engaging. A faulty thermostat, particularly in the context of the AUTO/FAN ON switch, might not interpret this setting correctly, causing it to work erratically. However, since the blower is running in the FAN ON position, it indicates that the switch is functioning as expected. The other options might imply a malfunction, but they do not fit the situation as neatly. A power supply issue or a blown fuse would typically result in no power to the blower motor at all; thus, if the blower is operational, these options would not apply. Additionally, a faulty compressor pertains to the cooling system and would not directly influence the operation of the blower when set to FAN