MG3P Installation Manual

54
FURNACE COMPONENTS
The descriptions below are various functional components that affect the operation and shutting down of this furnace. Some of
these components and their locations are shown in Figure 55. If any component of the furnace must be replaced, use only factory
authorized replacement parts specified in the Replacement Parts List provided online.
Blower Limit Switch - The Blower switch prevents furnace operation when blower is not operational.
Condensate Drain Switch - The Condensate Drain Switch will shut down the furnace if the condensate drain from the Collector
Pan becomes clogged.
Flame Sensor: The flame sensor verifies when a flame has carried over from the igniter to the opposite end burner. If no flame
is detected, the furnace will shut down within 4 seconds.
Flame Roll-Out Switch - The flame roll-out switch verifies that the burner flames are drawn into the heat exchanger tubes. If
the burner flames are not properly drawn into the heat exchanger, the flame roll-out switch will close the gas valve and initiate
the shutdown cycle.
Gas Valve - The gas valve controls the flow of gas to the burners. When the gas valve is energized it automatically opens and
regulates the gas pressure in the manifold.
Inducer Assembly - The inducer assembly vents products of combustion to the outside.
Pressure Switch - The pressure switch verifies that the inducer is drawing the combustion gases through the heat exchanger.
If the flame is not properly drawn into the heat exchanger tube, the rollout switch or the flame sensor will shut the furnace down.
Supply Air Limit Switch - The supply air limit switch prevents the air temperature leaving the furnace from exceeding the
maximum allowable outlet air temperature.
Figure 55. MG3(P,S) Component Locations
Blower
Assembly
Blower Door
Switch
Burner
Assembly
Control Board
Finish
Flange
Flame
Sensor
Gas Manifold
Gas Valve
Igniter
Inducer Assem
bly
Main Air Limit Switch
Pressure Switch
(Inducer)
Pressure
Switch - Condensate
(‘B’, ‘C’, & ‘D’ cabinets)
Roll-Out
Switch
Transformer
Vent Limit Switch
MG3P Series Upflow Gas Furnace
Burner
Assembly
Flame Sensor
Roll-Out
Switch
Blower Assembly
(behind blower panel)
Blower Door Switch
(behind blower panel)
Gas
Manifold
Gas Valve
Igniter
Inducer Assembl
y
Inducer Limit Switch
Furnace
Control
Board
Pressure Switch
Transformer
MG3S Series Downflow Gas Furnace
Finish
Flange