High Limit Control On A Gas Furnace

The limit switch includes a sensor in the heat exchanger to determine when the air is warm enough to circulate.

High limit control on a gas furnace.

Check with your owner s manual for suggested temperatures. Should the unit produce too much heat. The high limit switch in your gas furnace is a small part with two very important jobs. The high temperature limit switch is an important device used in forced air furnaces powered by gas or heating oil.

Once the air reaches a preset temperature the limit switch turns on the blower. Limit switches turn off the burner and turn on the circulating fan if there is a high temperature condition in the furnace. Set the markers to the appropriate settings for your furnace. For example if the blower motor stopped running then no air would move through the unit.

A limit switch is a device that s located under your furnace s supply plenum. But that s not the only thing that the high limit switch does. The hi limit switch will trip and shut down the heaters once the excess temperature setting is reached. For a general guide set the two lowest ones from the furthest left to 100 and 130 degrees to control when the fan comes on and goes off.

The limit switch shuts off the burner when the temperature exceeds a preset temperature. If the furnace oil or gas burner is very high capacity or if the furnace fan limit controls have been set to cause this effect the burner may on some systems cycle on and off periodically while the warm air blower continues to run. The switch makes sure the furnace is operating safely and at its desired settings. There is a difference between a limit switch and a rollout switch.

It reads the temperature of the plenum and waits until it gets appropriately warm. Turning the fan motor on and off is the high limit switch s main job. It s also known as a fan limit switch or simply a limit switch. The flames would raise the temperature inside the unit and have no place to go getting hotter and hotter.

Once the plenum reaches a specific temperature the limit switch sends a signal to the air handler to begin running and delivering warm air to your home. A high limit control switch will turn off the gas to a furnace if the temperature becomes too high. This is the role it plays in every cycle of your furnace s normal operation. The third marker should be set around 200 degrees as a safety shut off for the burner.

When the temperature reduces to normal the burner will come back on. Which way to set the white auto manual fan control switch.