In a conventional residential furnace, the high temperature limit switch is wired in series with which component?

In a conventional residential furnace, the high temperature limit switch is crucial for safe operation, as it prevents the system from overheating. This switch is wired in series with the gas valve, meaning that if the limit switch activates due to an over-temperature condition, it will interrupt the electrical circuit, closing the gas valve and thereby stopping the flow of gas to the burners. This safety feature ensures that the furnace does not operate under unsafe conditions which could lead to a fire or damage to the unit.

The high temperature limit switch should not be wired with components like the blower motor, ignition system, or pressure switch because these components operate under different conditions and functions. The blower motor, for instance, is responsible for circulating air and generally operates continuously during heating cycles, while the ignition system is involved in the starting process of the furnace. The pressure switch serves to ensure that the furnace is venting properly and the combustion air is adequate, which operates independently of temperature control. Therefore, the correct response indicates the connection necessary for maintaining safe furnace operation.