What safety device is commonly used to prevent overheating in an HVAC system?

The limit switch is a critical safety device in HVAC systems designed to prevent overheating. It acts as a safeguard by monitoring the temperature within the system. When the temperature exceeds a predetermined limit, the limit switch automatically interrupts the operation of the heating element or blower. This action ensures that the system does not overheat, which could cause damage to equipment or create dangerous conditions such as fires.

In comparison, a thermostat primarily regulates the desired temperature within a space by controlling the HVAC system's operation cycles but does not directly prevent overheating. The expansion valve is responsible for controlling the flow of refrigerant in systems, and while it plays a central role in cooling efficiency, it does not address overheating issues. The compressor relay is involved in cycling the compressor on and off, but it does not serve as a protective measure against excessive temperatures like the limit switch does.