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© 1998 Lennox Industries Inc.
Corp. 9801−L2
80MGF
Service Literature
Revised 08−2004
80MGF SERIES UNITS
80MGF series units are mid−efficiency gas furnaces
manufactured with tubular heat exchangers formed of alu-
minized or stainless steel. 80MGF units are available in
heating capacities of 45,000 to 140,000 Btuh and cooling
applications up to 5 tons. Refer to Engineering Handbook
for proper sizing.
Units are factory equipped for use with natural gas. A kit is
available for conversion to LPG operation. All 80MGF units
built proir to September 98 use electronic (direct spark) igni-
tion. 80MGF−11 model units are equipped with the Lennox
SureLight ignition system. The 80MGFX unit meets the
California Nitrogen Oxides (NO
x
) Standards and California
Seasonal Efficiency requirements. All units use a redun-
dant gas valve to assure safety shut−off as required by
A.G.A. or C.G.A.
The heat exchanger, burners and manifold assembly can
easily be removed for inspection and service by simply dis-
connecting gas, unplugging wiring harness and spark wires
and removing four screws holding the heat exchanger in
place. Then the heat exchanger slides out of the cabinet.
All specifications in this manual are subject to change.
Procedures outlined in this manual are presented as a rec-
ommendation only and do not supersede or replace local
or state codes. In the absence of local or state codes, the
guidelines and procedures outlined in this manual (except
where noted) are recommended only and do not constitute
code.
Units may be installed in upflow, downflow or horizontal
position. The heat exchanger is designed for upright or
horizontal use only. When the unit is installed in the down-
flow position, the heat exchanger is field removed and re-
installed so it is upright when the cabinet is inverted. No
field conversion is required when the unit is installed in the
horizontal position.
TABLE OF CONTENTS
Introduction 1. . . . . . . . . . . . . . . . . . . . . . . .
Specifications 2. . . . . . . . . . . . . . . . . . . . . .
Blower Data 5. . . . . . . . . . . . . . . . . . . . . . .
Parts Identification 7. . . . . . . . . . . . . . . . . .
I Unit Components 9. . . . . . . . . . . . . . . . . .
II Installation 19. . . . . . . . . . . . . . . . . . . . . . .
III Start Up 19. . . . . . . . . . . . . . . . . . . . . . . . .
Preliminary Seasonal Checks 20 . . . . .
Heating Start Up 20. . . . . . . . . . . . . . . .
IV Heating System Service Checks 20. . .
V Typical Operating Characteristics 22. . .
VI Maintenance 24. . . . . . . . . . . . . . . . . . . .
VII Wiring and Sequence of Operation 26.
VIII SureLight Control Troubleshooting 40.
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