The Pulse was a brand of Lennox furnace that has been replaced by more modern models, but was one of their primary gas furnace products in the 1980s. Because gas furnaces are not frequently replaced, homes may still have these residential furnaces. Pulse furnaces are basic heating systems that use gas as fuel source and heat according to their sizing. Three different types of Pulse furnaces produced varying levels of heat, but they all worked in the same way.
The Pulse uses a thermostat system to detect temperature and begin operation. This thermostat contains much of the circuitry in the system. It closes relays and transfers sensor data so the furnace can operate within the ranges set by the house owner. Problems with the wiring can keep the thermostat from correctly sensing temperatures both within the furnace and inside the home, preventing accurate operation.
The Pulse furnace brings in gas through a gas line of its own, connected to the primary supply for the house. This line has a gas valve that opens -- with orders from the thermostat -- and sends a steady supply of gas to the burner when necessary. Of course, combustion requires oxygen as well, so the Pulse also has a supply vent that brings in air to the combustion chamber.
The primary burner of the furnace only turns on when the furnace works, so it needs some type of ignition unit. The pilot light is a much smaller burner designed to keep lit and, when necessary light the gas flowing into the main burner, too. The pilot light has sensors, like the thermostat, that keep the Pulse from combusting too much gas and damaging the system.
The heat produced in the combustion chamber needs a way to reach the air. The furnace blower moves the air from the ductwork through the furnace. A metal component called the heat exchanger allows thermal energy to flow from its metal fins into the air. Heated, the air is pushed back out into the ductwork by the fan.