Gas Fitter Practice Test

How is a high limit tested on a forced warm air furnace?

1. By disconnecting the air circulating blower

2. By disconnecting the wire to the limit control

3. By disconnecting one wire on the thermostat when the furnace is warm

4. By shutting off the gas control so that the furnace will cool down

The correct answer is: By disconnecting the air circulating blower

Testing a high limit on a forced warm air furnace involves effectively checking the function of the limit switch, which is crucial for the safety and operation of the system. One effective method is to disconnect the air circulating blower. When the blower is disconnected, the high limit switch is triggered to ensure that the furnace does not overheat. If the high limit switch is functioning properly, it will cut off the power to the heating element when it reaches a predetermined temperature. This simulates a condition of overheating, allowing the technician to verify that the safety mechanism is working correctly. Testing in this way is important because it directly assesses the response of the limit switch under conditions likely to cause overheating. This method is also a practical approach, as it can be done in a controlled manner without putting the entire system at risk. While the other options offer various methods of testing or assessing the functionality of the furnace systems, they don't specifically evaluate the limit switch's ability to respond to overheating conditions like disconnecting the air circulating blower does.