Lennox G26Q3-50 - User Manual

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FIGURE 1
G26 FURNACEY
AG26 HEAT EXCHANGE ASSEMBLY
Combustion Process:
1. A call for heat starts the combustion air blower.
2. Outdoorairisdrawnthroughpipeintotheburner
compartment where it mixes with gas in a con-
ventional style inshot burner.
3. TheSureLightignitionsystemlightstheburners.
4. Combustion products are drawn downward
through the heat exchanger. Heat is extracted
as indoor air passes across the outside surface
of the metal.
5. Latent heat is removed from the combustion
productsasairpassesthroughthecoil.Conden-
sate (water) is formed as the combustion prod-
ucts cool.
6. As the combustion products exit the coil, con-
densate is collected and drained away.
7. Combustion products are pulled from the heat
exchanger and forced into the flue.
7
5
4
6
2
3
1
Page 1
ã 1997 Lennox Industries Inc.
Litho U.S.A.
Corp. 9721-L11
G26
Service Literature
Revised 07-2001
G26 SERIES UNITS
G26 series units are high-efficiencyupflow gas furnaces manufactured with
DuralokPlust aluminized steel clamshell-type heat exchangers. G26 units
are available in heating capacities of 50,000 to 125,000 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 con-
version to LPG operation. G26-1 and -2 model units use electronic (intermit-
tent pilot) ignition. G26-3, -4, -5 and -6 model units feature the Lennox Sur-
eLightT silicon nitride ignition system. Each unit meets the California Nitro-
gen Oxides (NO
x
) Standards and California Seasonal Efficiency require-
ments without modification. All units use a redundant gas valve to assure
safety shut-off as required by A.G.A. or C.G.A.
Information contained in this manual is intended for use by qualified service
technicians only. All specifications are subject to change. Procedures out-
lined in this manual are presented as a recommendation only and do notsu-
persede 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.

Summary

G26 Series Units Overview

Unit Components and Orientation

SureLight Ignition System

Control Board, Diagnostics, and Terminals

Details the SureLight control board, terminal designations, and diagnostic codes.

Pilot, Flame Sensor, and Gas Valve

Pilot Assembly and Gas Valve Operation

Combustion Air System and Pressure Switches

Differential Pressure Switch Operation

Condensate Management

Condensate Piping and Removal Process

Unit Start-Up and Service Checks

Heating Start-Up and Gas Pressure Testing

Covers heating start-up procedures, gas pressure testing, and CO2/CO checks.

Cleaning Procedures

Heat Exchanger, Burner, and Blower Cleaning

Provides step-by-step instructions for cleaning the heat exchanger and burners.

Wiring Diagrams and Operation Sequences

Field Wiring and Thermostat Connections

Shows typical field wiring diagrams and thermostat connection designations.

Operation Sequences

Heating Sequence - SureLight Control

Cooling Sequence of Operation

Fan Operation Sequences

Troubleshooting Guides

SureLight Control Troubleshooting

Guides troubleshooting for unit failures in cooling, heating, or fan modes.

Burner Ignition and Shutdown Issues

Troubleshoots issues where burners light but the unit shuts down prematurely.

Control Signals and Blower Operation

G776 Ignition Control Troubleshooting

Pilot Not Lighting or Main Valve Not Opening

Troubleshooting guide for when the pilot will not light but spark is present.

Lennox G26Q3-50 Specifications

General

Efficiency	80%
Input BTU	50, 000
Stages	Single-stage
Heating Capacity	40, 000 BTU
AFUE Rating	80%
Blower Motor Type	PSC
Ignition Type	Hot Surface Ignition
Blower Motor	PSC
Gas Valve Type	Single-stage
Vent Size	4 inch