Lennox G26Q4/5-75 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.

Lennox G26Q4/5-75 Specifications

General

Model	G26Q4/5-75
Type	Gas Furnace
Efficiency Rating	80% AFUE
Blower Type	Multi-speed
Fuel Type	Natural Gas
Stages	Single Stage
Input BTU	75, 000 BTU
AFUE Rating	80%
Blower Motor Type	PSC
Heat Exchanger Material	Aluminized Steel
Filter Type	Standard
Weight	135 lbs
Heating Capacity	75, 000 BTU/h

Summary

G26 SERIES UNITS

Unit Description

Overview of the high-efficiency upflow gas furnaces and their capabilities.

SPECIFICATIONS

Model Specifications

Ignition System and Controls

SureLight Ignition System

Information on the SureLight ignition system for models -3 through -6.

SureLight Control Board Details

Terminal Designations and Diagnostics

Safety Precautions and Blower Motors

Electrostatic Discharge (ESD) Precautions

Ignition Control Operation (-1 and -2 Models)

Unit Operation Sequence

Ignition Components and Troubleshooting LEDs

Pilot, Spark Electrode, Flame Sensor

Arrangement and function of ignition system components.

Differential Pressure Switch (S64)

Switch Operation and Circuitry

Start-Up Procedures

Preliminary and Seasonal Checks

Heating Start-Up Steps

Steps for safely starting the furnace for heating operation.

Gas Pressure Testing and Checks

Testing Gas Supply Pressure

Gas Flow and Flame Signal Measurement

Flame Signal Measurement

Cleaning Heat Exchanger and Burners

Heat Exchanger Cleaning Process

Detailed steps for cleaning the heat exchanger and burners.

Wiring Diagrams and Sequences

Field Wiring and Thermostat Connections

Diagram showing thermostat wiring connections to the furnace.

Heating Sequence of Operation

Normal Heating Mode

Flowchart detailing the normal heating sequence steps.

Cooling Sequence of Operation

Normal Cooling Mode

Flowchart detailing the normal cooling sequence steps.

SureLight Control Troubleshooting Guide

Problem 1: Unit Fails to Operate

Troubleshooting steps for units failing to operate in any mode.

Troubleshooting Ignition and Burner Issues

Problem 6: Burners Light but Shut Down Prematurely

Troubleshooting when burners light but shut down prematurely.

G776 Ignition Control Troubleshooting

Spark Present, Pilot Not Lighting

Troubleshooting steps when spark is present but pilot fails to light.