1998 Lennox Industries Inc.
Litho U.S.A.
Page 1
Corp. 9703-L2
G27M
Service Literature
Revised 05-2000
G27M SERIES UNITS
G27M series units are mid-efficiency gas furnaces
manufactured with tubular aluminized steel heat ex
changers. G27M units are available in heating capaci
ties of 60,000 to 120,000 Btuh (17.6 to 35.2 kW) and cool
ing applications from 1.5 through 5 tons (3.5 through
17.6 kW). Refer to Engineering Handbook for proper siz
ing.
Units are factory equipped for use with natural gas only.
LP kits are not available. All G27M units feature the Len
nox SureLight hot surface ignition system. The
G27MX units meet the California Nitrogen Oxides (NO
x
)
Standards and California Seasonal Efficiency require
ments. All units use a two-stage gas valve along with a
two-stage induced draft blower assembly. The gas
valve is redundant to assure safety shut-off as required
by A.G.A. and C.G.A.
Units may be installed in upflow, downflow or horizon
tal position. The heat exchanger is designed for upright
or horizontal use only. When the unit is installed in the
downflow position, the heat exchanger must be field
removed and reinstalled so it is upright when the cabi
net is inverted. No field conversion is required when
the unit is installed in the horizontal position.
The heat exchanger, burners and manifold assembly
can easily be removed for inspection and service by sim
ply disconnecting gas, unplugging wiring harnesses
and removing four screws holding the heat exchanger in
place. The heat exchanger slides out of the cabinet.
Information contained in this manual is intended for use
by qualified service technicians only. All specifications
are subject to change. Procedures outlined in this manu
al are presented as a recommendation only and do not
supersede or replace local or state codes.
G27M
TABLE OF CONTENTS
General 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Specifications 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Blower Performance Data 2. . . . . . . . . . . . . . . . . . . . .
I-Unit Components 4. . . . . . . . . . . . . . . . . . . . . . . . . . .
II-Placement and Installation 11. . . . . . . . . . . . . . . . . .
III-Start-Up 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IV-Heating System Service Checks 12. . . . . . . . . . . .
V-Typical Operating Characteristics 14. . . . . . . . . . . .
VI-Maintenance 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VII-Wiring Diagram and Sequence of Operation 17
VIII-Troubleshooting 23. . . . . . . . . . . . . . . . . . . . . . . . .
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