What is the main function of the main limit switch?

What is the main function of the main limit switch?

The primary limit switch is a temperature-activated sensor that protects your furnace from overheating whenever the fan fails to blow enough air over the heat exchanger. The limit switch also controls when the blower assembly turns on and off.

How do I know if my limit switch is bad on my furnace?

Limit Switch Malfunctions One common symptom of a malfunctioning limit switch is a blower fan that doesn’t shut off. This happens when the switch fails to shut off after the burners have stopped and the air exchanger is sufficiently cool. A bad switch also can prevent a furnace from operating at all.

What does a limit control do?

A limit switch is a device that’s located under your furnace’s supply plenum. A limit switch also acts as a safety device for your furnace. If the temperature inside of the plenum gets too hot, it shuts off the gas supply to your burners to prevent your furnace and heat exchanger from overheating.

What is the purpose of a high limit switch?

Turning the fan motor on and off is the high limit switch’s main job. This is the role it plays in every cycle of your furnace’s normal operation. But that’s not the only thing that the high limit switch does. It’s also safety device that helps prevent your furnace from overheating.

What safety function does the limit switch perform?

While the primary function of the limit switch is to turn the blower fan on and off, it also has a safety role. When the temperature in the air supply plenum gets too hot, the limit switch turns off the furnace boiler to keep there from being any damage from overheating.

What does limit switch open mean?

Limit switch codes If the furnace failure code indicates an “open limit” or “open high temperature switch” or “open rollout switch”, it is probable that the furnace has overheated. Limit switches turn off the burner and turn on the circulating fan if there is a high temperature condition in the furnace.

How do you diagnose a bad limit switch?

With the furnace in full operation, connect a digital voltmeter across the two connections of the limit switch. The voltage drop should be less than or a maximum of 0.1 VDC. The switch should be immediately suspect if the voltage drop is 0.2 VDC or higher (Fig. 1 indicates a bad limit switch).

Why does my limit switch keep tripping?

If the air inside your furnace gets too hot, the limit switch trips to prevent overheating. If the furnace high limit switch trips due to overheating, there is likely an airflow issue that is preventing proper air movement through the system. A dirty filter is the most common cause of airflow issues.

How does a limit switch work on an air conditioner?

It reads the temperature of the plenum and waits until it gets appropriately warm. 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 limit switch also acts as a safety device for your furnace.

What does the fan limit switch do on a furnace?

Also known as the fan limit switch or simply the limit switch, it has two functions in the furnace’s operation: It turns the fan on and off during the normal heating cycles of the furnace, and it senses heat and shuts down the furnace if the interior temperature gets too high.

What happens when a limit switch is too high?

If a limit switch (doing its job) hits its top limit and has to shut off the burner four or so times, the control computer of the furnace may go into a “hard shutdown” mode so that the furnace won’t turn on until the unit is serviced.

What is a high-temperature limit switch?

The high-temperature limit switch is a small but important device used in forced-air furnaces powered by natural gas, LP, or heating oil.