How does a limit switch work on a furnace?
A furnace is an essential component of a heating system, providing warmth and comfort during cold weather. One of the critical safety features of a furnace is the limit switch. This device plays a crucial role in ensuring the safe operation of the furnace and preventing potential hazards. In this article, we will explore how a limit switch works on a furnace and its significance in maintaining a safe and efficient heating system.
The limit switch is a type of switch that is designed to monitor and control the temperature inside the furnace. It is typically mounted on the furnace’s heat exchanger, which is the part responsible for transferring heat from the combustion process to the air that is distributed throughout the home. The limit switch consists of a bimetallic strip, a relay, and a set of contacts.
When the furnace operates, the heat exchanger becomes hot due to the combustion process. The limit switch is designed to detect any abnormal rise in temperature. If the temperature exceeds a predetermined threshold, the bimetallic strip inside the switch will bend due to the differential expansion caused by the heat.
The bimetallic strip is made of two different metals with different coefficients of thermal expansion. When heated, one metal expands more than the other, causing the strip to bend. This bending action triggers the relay, which in turn opens or closes the electrical contacts.
There are two types of limit switches commonly used in furnaces: the high-limit switch and the low-limit switch.
1. High-limit switch: This switch is designed to protect the furnace from overheating. When the temperature inside the furnace exceeds the safe operating range, the bimetallic strip bends, triggering the relay to open the contacts. This action interrupts the electrical circuit, shutting down the furnace and preventing any further damage.
2. Low-limit switch: This switch is responsible for maintaining the minimum temperature inside the furnace. If the temperature drops below a certain level, the bimetallic strip will bend, triggering the relay to close the contacts. This action allows the furnace to restart and continue heating the home.
The limit switch is an essential safety feature that helps prevent several potential hazards, such as:
– Overheating: By shutting down the furnace when the temperature exceeds the safe operating range, the limit switch prevents the heat exchanger from becoming too hot, which could lead to a fire or other damage.
– Carbon monoxide buildup: If the furnace does not receive enough air for combustion, carbon monoxide can build up inside the home. The limit switch can detect this condition and shut down the furnace to prevent carbon monoxide poisoning.
– Malfunctioning furnace: In some cases, the furnace may malfunction and not shut down when it should. The limit switch can detect these issues and shut down the furnace to prevent further damage.
In conclusion, the limit switch is a vital component of a furnace that helps ensure the safe and efficient operation of the heating system. By monitoring and controlling the temperature inside the furnace, the limit switch plays a crucial role in preventing potential hazards and maintaining a comfortable and safe environment in your home.
