Lennox 47K18 400F M/R SPST Rollout Switch

The Lennox 47K18 400F M/R SPST Rollout Switch is an essential safety device in Lennox heating and cooling systems especially the gas furnaces. It is an SPST switch that is supposed to cut off the supply of gas in the case of high temperatures. This is usually mounted on the outside of the furnace and has a heat activated spring. When the temperature of the furnace goes high, which is not safe in this case being 400 degrees Fahrenheit, the spring also opens the switch. This shuts down the gas supply restricting further temperature rise and some other actual dangers such as heat endangerment and fire.