Limit Switches Explained: Applications in HVAC, Industrial, and Home Use

In the field of electrical components, limit switches are one of those parts you never think about until one fails. And when it does, the results can range from system downtime to safety hazards. In HVAC systems, a failed limit switch can cause a furnace to overheat, shut down unexpectedly, or stop the blower from running at the right time. 

In industrial automation, it can bring an entire production line to a halt. That’s why technicians choose the right type for the application, rated correctly for voltage, pressure, and environmental conditions.

The technicians who minimize callbacks and repeat failures are the ones who match the switch to the system’s exact demands. This guide will walk you through what a limit switch is, how it functions in HVAC, industrial, and home applications, what to know about furnace-specific limit switches, and which proven models deliver reliable performance in the field.

What is a Limit Switch?

A limit switch is an electromechanical device that detects the position or condition of a moving part and sends an electrical signal to control equipment accordingly. In other words, it “limits” motion by activating or deactivating a circuit when a set condition is met.

Depending on design, a limit switch may sense:

• Physical contact (mechanical switches)

• Airflow or pressure changes

• Temperature thresholds

• Magnetic or optical position

The advantage is simple: they act as an interface between moving parts and control systems, ensuring operations happen within safe and efficient boundaries.

How a Limit Switch Works

Inside a limit switch, an actuator is linked to a set of electrical contacts. When the actuator moves whether by being pressed, pushed, rotated, or sensing a change in airflow or pressure, it opens or closes the circuit. This signal is then interpreted by the control system, triggering actions like:

• Stopping a motor

• Starting a fan

• Shutting down a heater

• Activating an alarm

In HVAC, for example, a pressure limit switch might halt a furnace if airflow drops below safe levels, preventing overheating.

Applications of Limit Switches

Limit switches appear in more places than you might expect. Here’s where they make a critical difference:

HVAC Systems

In heating and cooling systems, limit switches protect components from damage and maintain comfortable, safe operation. They:

• Detect overheat conditions in furnaces

• Sense airflow in duct systems

• Monitor refrigerant or air pressure

• Control blower fans based on temperature

Example from Voomi Supply: The RGF HLED-AS Air Sensing Switch Kit is designed for HALO-LED systems, detecting airflow with precision in HVAC setups. Operating on 24 VAC and mounted vertically, it’s ideal for maintaining indoor air quality and ensuring system components only run under proper airflow conditions.

Industrial Machinery

In manufacturing, limit switches detect position and movement, often providing safety interlocks. They can:

• Stop conveyors when items reach a certain point

• Verify machine guards are closed before operation

• Control actuator travel distance

Home Appliances

Limit switches also appear in microwaves, garage doors, washing machines, and dryers, where they confirm door closure, control motion limits, and prevent overheating.

What is a Limit Switch on a Furnace?

A limit switch on a furnace monitors temperature within the heat exchanger. If the air inside gets too hot, it shuts down the burners to prevent overheating. This is both a safety measure and a way to extend equipment lifespan.

Many furnaces also use pressure limit switches to verify that fans and vents are moving air correctly. Without this safeguard, a blocked vent or failed blower could cause dangerous heat buildup.

Examples from Voomi Supply:

• The Goodman 24V Air Pressure Switch (11177113) regulates air pressure in gas furnaces like the Amana AMV90453BX. By maintaining proper airflow and pressure levels, it prevents unsafe operating conditions. Its durable build and easy installation make it a favorite for both service technicians and homeowners.

• The Lennox 86M36 High Pressure Switch protects HVAC equipment by monitoring pressure levels and preventing operation outside safe limits—critical for maintaining performance and avoiding costly repairs.

Furnace Fan Limit Switch

A furnace fan limit switch specifically controls when the blower fan turns on and off:

• Turns the fan on when the furnace reaches the fan-on temperature (around 120-140 °F)

• Keeps it running until the temperature drops below the fan-off setting (around 90-100 °F)

• Shuts down the furnace if a high-limit temperature (around 200 °F) is reached

Automating blower operation improves efficiency and safety.

Types of Limit Switches

Common categories include:

• Mechanical (lever, roller, plunger types)

• Air pressure switches (used in HVAC airflow monitoring)

• Temperature limit switches (overheat prevention)

• Non-contact switches (magnetic, inductive, optical)

• Specialty switches (momentary-action air switches, disconnects)

Examples from Voomi Supply:

• The Herga 6871-OCO-U126 Air Switch features SPDT operation with momentary action, offering precise control in air-operated equipment. Its threaded center spout makes installation straightforward in tight setups.

• The Diversitech DPB222R Disconnect Box (60 A, 240 V, non-fusible) provides a safe, reliable means of isolating power for HVAC maintenance—an essential step when replacing or servicing limit switches.

• The Trane RLY03211 Start Relay (50 A, 240 V) ensures robust startup performance in compatible Trane systems, working alongside limit switches to maintain reliable HVAC operation.

Choosing the Right Limit Switch

When selecting a limit switch, consider:

• Application type (HVAC, industrial, appliance)

• Sensing method (mechanical, airflow, pressure, temperature)

• Electrical rating (voltage, amperage)

• Mounting style (vertical, horizontal, threaded, panel-mounted)

• Environment (temperature extremes, moisture, dust)

At Voomi Supply, with every limit switch we offer, you can get the right part exactly when you need it.

Limit Switch Essentials Every Technician Should Know

Limit switches are the front line of protection and control in HVAC, industrial machinery, and even home appliances. In this guide, we covered:

• What a limit switch is and how it works to translate physical or environmental conditions into control signals.

• Furnace-specific applications, including high-limit and fan limit switches, safeguard against overheating and optimize blower operation.

• Key types: from mechanical to pressure, air-sensing, and temperature-based designs.

• Real-world solutions using dependable models like the RGF HLED-AS for airflow sensing, Goodman 11177113 and Lennox 86M36 for furnace safety, Herga 6871-OCO-U126 for precise air control, Diversitech DPB222R for safe disconnecting, and Trane RLY03211 for reliable startup control.

In practice, the right limit switch prevents costly damage, ensures compliance with safety standards, and keeps systems operating smoothly. Voomi Supply doesn’t just stock parts - we curate reliable, field-tested Relays & Switches so HVAC pros, maintenance crews, and skilled homeowners can solve problems quickly, with components they trust to perform.