This Reznor limit switch is a safety device designed to monitor temperature and activate when a specific threshold is reached, in this case, 135 degrees Fahrenheit. It functions as a manual reset (M/R) component, meaning that it requires user intervention to reset the switch once it has been triggered. This feature ensures that the system does not automatically restart without addressing the condition that caused the over-temperature situation, providing an additional layer of safety. The switch is typically used in HVAC systems and other equipment where temperature regulation is critical for safe operation.