Lennox G26Q2-50 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.

Lennox G26Q2-50 Specifications

General

Brand	Lennox
Model	G26Q2-50
Category	Furnace
Language	English

Summary

G26 SERIES UNITS

G26 FURNACE HEAT EXCHANGE ASSEMBLY

Explains the combustion process of the G26 furnace, detailing the steps from call for heat to flue gas expulsion.

BLOWER PERFORMANCE DATA

BLOWER PERFORMANCE DATA (Continued)

G26-3 THROUGH -6 COMPONENTS

G26 Components Overview

Illustrates and labels the various components of the G26-3 through -6 models.

G26 GENERAL PARTS ORIENTATION

Furnace Components Diagram

Provides a general overview and labeling of the main parts and components within the G26 furnace.

Control Box Components and Functions

SureLight Ignition System A3 (-3 through -6 models)

Explains the SureLight ignition system, its components, and its function in furnace ignition.

SURELIGHT CONTROL BOARD

SureLight Control Terminal Designations

Lists the terminal designations for the SureLight control board and their corresponding functions.

Diagnostic Codes for Control Board

Provides diagnostic codes related to LED indicators and their troubleshooting meanings.

SureLight Board Terminal Designations

Electrostatic Discharge (ESD) Precautions

Outlines safety precautions for handling electronic components to prevent damage from electrostatic discharge.

Electronic Ignition Process

Diagnostic LED Function

Furnace Control A3 Diagnostic LED

Shows the diagnostic LED states, their meanings, and remedies for troubleshooting.

Johnson G776 Ignition Control Operation

Explains the operation of the Johnson G776 ignition control for heating and abnormal modes.

Pilot, Spark Electrode, Flame Sensor (-1 and -2 models)

Differential Pressure Switch (S64)

Combustion Air Prove Switch Function

Describes the differential pressure switch, its function, and how it monitors combustion air blower operation.

Measuring Pressure Differential

Pressure Switch Troubleshooting Chart

Explains how to measure pressure differential and the importance of the 0.2-inch differential.

Heating Start-Up Procedures

Safe Lighting Instructions

Provides instructions for safely starting up the furnace for heating operation.

Gas Valve Operation Guide

HEATING SYSTEM SERVICE CHECKS

Testing for High CO2 and CO

Testing Gas Piping

Gas Supply Pressure Testing

Testing Gas Supply Pressure

Explains how to test the gas supply pressure at the unit and acceptable ranges.

Manifold Pressure Check

Describes how to measure and check the manifold pressure for proper unit operation.

Gas Flow and Pressure Checks

Flame Signal Measurement

Details how to measure the flame signal using a DC meter and transducer.

Typical Operating Characteristics

External Static Pressure Measurement

Blower Speed Taps Leadless Motors

B-Cleaning Heat Exchanger and Burners

Heat Exchanger Cleaning Procedure

Provides detailed procedures for cleaning the heat exchanger and burners, including disassembly steps.

VII-WIRING DIAGRAM, SEQUENCE OF OPERATION &TROUBLESHOOTING

Field Wiring and Thermostat Connections

Illustrates typical field wiring diagrams and thermostat connections for G26 models.

G26 Wiring Diagrams

Wiring Diagram G26 (-3 & -4 Shown)

Provides the wiring diagram for G26 models, showing electrical connections for components.

HEATING SEQUENCE OF OPERATION SURELIGHT CONTROL

Normal Heating Mode Sequence

Details the normal heating sequence of operation for the SureLight control.

Abnormal Heating Mode Sequence

Outlines abnormal heating modes and corresponding LED diagnostic codes.

COOLING SEQUENCE OF OPERATION SURELIGHT CONTROL

Normal Cooling Mode Sequence

Describes the normal sequence of operation for the SureLight control during cooling mode.

Abnormal Cooling Mode Sequence

Details abnormal cooling modes and the corresponding diagnostic LED indications.

SureLight Control Troubleshooting Guide

Unit Operation Failures

Addresses issues where the unit fails to operate in any mode, with diagnostic light indications.

Combustion Air Blower Continuous Operation Issues

Troubleshoots issues with continuous combustion air blower operation but no heating/cooling.

Combustion Air Blower Not Energizing in Heating

Troubleshoots failure of the combustion air blower to start in heating mode.

Heating Failure: Ignitor Not Energized

Heating Failure: Ignitor Not Energized

Troubleshoots failure to fire in heating mode when the combustion air blower energizes but the ignitor does not.

Heating Failures: Ignitor Energized

Burners Light but Shut Down Prematurely

Addresses burners lighting but the unit shutting down prematurely, indicated by pressure switch codes.

Control Signals Low Flame Sense

Troubleshoots low flame sense signals during heating mode, indicated by diagnostic lights.

Indoor Blower Failure to Operate

Troubleshoots failure of the indoor blower to operate in any mode.

BCC2 Blower Control Troubleshooting

BCC2 Troubleshooting Flowchart

A flowchart to guide troubleshooting for the BCC2 blower control on -1 and -2 models.

G776 Ignition Control Troubleshooting

Spark Present but Pilot Will Not Light

Troubleshooting guide for situations where the pilot will not light despite spark presence.

G776 Ignition Control Troubleshooting (Continued)

No Spark and System Will Not Work

Troubleshooting steps for when there is no spark and the system fails to operate.

Pilot Lights but Main Valve Will Not Come On

Troubleshooting steps for when the pilot lights but the main valve does not activate.