Lennox G26Q4/5-125 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 G26Q4/5-125 Specifications

General

Brand	Lennox
Model	G26Q4/5-125
Category	Furnace
Language	English

Summary

G26 SERIES UNITS

G26 FURNACE HEAT EXCHANGE ASSEMBLY

I-UNIT COMPONENTS

A-Make-Up Box

B-Control Box Components

Identifies and describes the components found within the G26 control box.

Control Box Components

3- Door Interlock Switch (S51)

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

Details the SureLight ignition system, its components, and operation.

E-G26-1 and -2 Models

12-Ignition Control (-1 and -2 models)

Details the intermittent pilot ignition control for specific G26 models.

Diagnostic LED

Johnson G776 Ignition Control Operation

Explains the operational sequence and LED indicators for the ignition control.

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

TYPICAL BURNER PILOT/ELECTRODE ORIENTATION

14-Gas Valve

Details the gas valve types, their safety features, and replacement.

15-Differential Pressure Switch (S64) (Combustion Air Prove Switch)

DIFFERENTIAL PRESSURE SWITCH CIRCUITRY

IV-HEATING SYSTEM SERVICE CHECKS

To Turn Off Gas To Unit

Step-by-step instructions for safely turning off the gas supply to the unit.

C-Safety or Emergency Shutdown

Procedures for immediate shutdown in case of safety concerns.

D-Testing Gas Piping

E-Testing Gas Supply Pressure

F-Check Manifold Pressure

Explains how to check and adjust manifold pressure for proper unit operation.

G- Proper Gas Flow (Approximate)

I-Flame Signal

Details how to measure the flame signal for ignition troubleshooting.

BURNER ACCESS/REMOVAL

Simplified Burner Removal

Cleaning the Burner Assembly

VII-WIRING DIAGRAM, SEQUENCE OF OPERATION &TROUBLESHOOTING

A-Field Wiring, Thermostat Connections

D- SureLight Control Trouble Shooting Guide

PROBLEM 1: UNIT FAILS TO OPERATE IN THE COOLING, HEATING, OR CONTINUOUS FAN MODE

Troubleshooting for units failing to operate in any mode, with diagnostic light codes.

PROBLEM 2: UNIT FAILS TO OPERATE IN THE COOLING OR HEATING MODE, BUT COMBUSTION AIR BLOWER OPERATES CONTINUOUS.

Troubleshooting for units operating in cooling but not heating, with specific blower cycling.

PROBLEM 3: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER DOES NOT ENERGIZE

Troubleshooting for units not starting combustion air blower during heating.

PROBLEM 4: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER ENERGIZES, IGNITOR IS NOT ENERGIZED.

Troubleshooting for units failing to fire, with ignitor not energizing.

PROBLEM 5: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER ENERGIZES, IGNITOR IS ENERGIZED. (CONT.)

Troubleshooting for units failing to fire, with ignitor energized but no ignition.

PROBLEM 6: BURNERS LIGHT WITH A HEATING DEMAND BUT UNIT SHUTS DOWN PREMATURELY

Troubleshooting for burners lighting but shutting down prematurely.

PROBLEM 6: BURNERS LIGHT WITH HEATING DEMAND BUT UNIT SHUTS DOWN PREMATURELY (CONT.)

Troubleshooting for burners lighting but shutting down prematurely.

PROBLEM 7: CONTROL SIGNALS LOW FLAME SENSE DURING HEATING MODE

Troubleshooting for control signaling low flame sense during heating operation.

PROBLEM 8: INDOOR BLOWER FAILS TO OPERATE IN COOLING, HEATING, OR CONTINUOUS FAN MODE

Troubleshooting for the indoor blower failing to operate in any mode.

PROBLEM 9: RF STATIC DURING TIME FOR IGNITION

G-G776 Ignition Control -1 and -2 Models

Spark is present but pilot will not light

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

G776 IGNITION CONTROL TROUBLESHOOTING -1 and -2 MODELS

No spark and system will not work

Troubleshooting steps when no spark is produced and the system does not operate.

Pilot lights but main valve will not come on

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