HVAC Tools and Tips – Lennox Furnace Guide

Homeowners and do-it-yourselfers are often confused about what can and can’t be done to repair Lennox HVAC furnace parts. This guide explains how a typical Lennox furnace works and includes a few fixes. First of all, the furnace operates automatically and is controlled by a thermostat so that when the temperature is set using the thermostat, the furnace will only kick on when the ambient temperature is lower than the thermostat setting.

In more detail: when the temperature drops below the thermostat setting, the transformer powers up the fan control board. Then the fan control board powers up the induced draft blower motor. At this point, a P1 pressure switch kicks in the ignition, giving energy to the pilot gas valve, which is then lit. Once the ignition control sensors register pilot flame ignition, the main valve is opened and all burners are lit by the flame. It takes about thirty seconds for the electronic fan control (this is not adjustable) to turn on the blower and then for the blower to push air across the heat source. It is then that the heat begins to move into and by the ductwork, bringing warmth to the rooms. Once the temperature is again at the level set on the thermostat, the electric circuit shuts down, the main gas valve stops the flow of gas to the burners, and the blower runs for a preset (this is adjustable) time period.

This is where HVAC tools and tips can come in handy, because the description above tells you how the Lennox HVAC furnace is supposed to work. When there is a malfunction, the furnace will begin to cycle according to a heat sensing limit switch instead of being controlled by the thermostat. So, if a furnace should overheat-in other words, when the thermostat’s control is no longer functional-the heat sensing switch keeps the furnace from running perpetually and overheating. It works in this way: The limit switch opens. It cuts off the main gas valve circuit, which stops the heat; then the furnace unit cools by way of a blower motor. Once everything has cooled sufficiently, the limit switch is deactivated, and when the unit is again at a normal temperature level and the limit switch has closed, the main burner will relight. Overheating and issues with the thermostat are signs that a technician should be called on to restore normal functioning.

Final tip about maintenance: Be aware that motor and blower assemblies that are direct-excursion don’t need to be oiled; they’re lubricated during manufacturing. However, lubrication of the blower motor may be required. A qualified HVAC Lennox technician who has the correct HVAC tools and knowledge can take care of this task safely and effectively.

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