Limit Switch

Limit switches are used to detect the presence of a moving object when the object passes or when it reaches its final destination. Limit switches, also known as limit sensors, allow the user to regulate the operation of a machine equipped with moving parts, connected to a switching action mechanism. Limit switches for furnaces are a component of a forced-air furnace that is responsible for turning on the furnace blower once the desired heat has been met inside the furnace. Without a limit switch, a furnace wouldn't be able to control the temperature in conjunction with a thermostat. A high limit switch (also known as a furnace plenum thermostat) is a safety device on a furnace that is designed to cut the gas supply when the burner temperature exceeds the safe operating range. When the temperature goes back to normal, it will let the valve open again.

Types of Limit Switches

There are 4 general limit switch types: whisker, roller, lever, and plunger. A whisker switch is a high-quality, multi-directional contact switch with a plastic-coated spring-rod whisker. A rollout switch is a safety device that is designed to detect flame rollout and shut off the gas valve when that happens. The micro limit switch is a different type of limit switch usually found on control circuits. These types of switches are much smaller than their standard counterparts, which lets them be installed in narrow or little spaces that would normally be too small for other switches. Plunger switches operate with little physical force. When the plunger is pressed, it either opens or closes the electrical circuit turning the device on or off.

Is Honeywell Worth It?

A Honeywell fan limit switch controls when the furnace blower fan turns on and off. A Honeywell limit switch is recognized as a good product in the industry. They are known for being reliable and safe to use as well as being designed to withstand the toughest of industrial applications.