What is the best way to test the limit switch on a furnace after installing a fan control center?

Testing the limit switch on a furnace after installing a fan control center is crucial for ensuring the system functions safely and effectively. The correct approach involves disabling the blower, setting the thermostat to call for heat, and turning the fan switch to 'on.'

This method allows for a direct assessment of the limit switch's functionality by observing whether it properly responds to heat conditions. When the thermostat is set to call for heat, the furnace will attempt to ignite and heat the chamber. If the temperature exceeds the limit switch's preset threshold, the switch should open, cutting power to protect the furnace from overheating. By having the blower disabled, you can avoid potential interference from airflow, ensuring the limit switch's cycling is clearly visible. Turning the fan switch to 'on' prioritizes checking the limit switch without introducing external variables that could affect the furnace's operation.

The situation described in other options would not effectively test the limit switch. Observing operation without any active testing does not provide insights into the limit switch's effectiveness. Also, activating the blower while setting the thermostat to cool would not accurately engage the furnace or the limit switch in any way relevant to heat conditions. Measuring voltage across the limit switch, while it might offer some diagnostic information, is not a comprehensive test