Goodman 1370906 Primary Limit Switch 150 Degrees. Among the number of safety devices built-in to a furnace is the limit switch. The main duty of a limit switch is to shut the burners down. Should the heat exchanger temperature get too hot, it would crack.
The main limit switch is a 1/2” disc designed to shut off the burner gas should the outlet (bonnet) temperature exceed the maximum design outlet air temperature. This switch is not adjustable. To check the operation, block the return air flow through the unit temporarily. The limit switch should function and shut the burner gas off within a few minutes. Remove the blockage and allow the switch to cool sufficiently before reestablishing burner flames.