Gas Fitter Practice Test

What device is the high temperature limit switch in the circuitry of a residential furnace wired in series with?

1. Fan motor

2. Manual fan switch

3. Gas valve

4. Summer/winter switch

The correct answer is: Gas valve

The high temperature limit switch is an essential safety device in the circuitry of a residential furnace, and it is designed to prevent overheating by shutting off the operation of the furnace when excessive temperatures are detected. In this context, wiring the high temperature limit switch in series with the gas valve is crucial because it directly controls the flow of gas to the burners. When the high temperature limit switch detects that the furnace is operating above its safe temperature threshold, it opens its circuit, interrupting power to the gas valve and effectively stopping the flow of gas to the burners. This operation is vital for ensuring safety, as it prevents potential hazards such as fires or equipment damage due to overheating. Therefore, the correct answer highlights the relationship between the high temperature limit switch and the gas valve within the furnace's safety mechanisms. The other devices mentioned, such as the fan motor, manual fan switch, and summer/winter switch, operate under different functions and wouldn't be directly shut off by the limit switch in response to overheating. These components have their own operational roles, separating them from the direct safety function associated with the gas supply controlled by the limit switch.