Lennox G26Q3/4-125 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 G26Q3/4-125 Specifications

General

Brand	Lennox
Model	G26Q3/4-125
Category	Furnace
Language	English

Summary

G26 SERIES UNITS

G26 FURNACE G26 HEAT EXCHANGE ASSEMBLY

Explains the combustion process and heat exchange assembly.

BLOWER PERFORMANCE DATA

I-UNIT COMPONENTS

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

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

ELECTROSTATIC DISCHARGE (ESD)

Precautions and Procedures

Details electrostatic discharge precautions and procedures for safe handling.

BLOWER CONTROL A15 TERMINAL DESIGNATIONS

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

Measuring pressure differential

Condensate Piping

G26-3 THROUGH -6 MODEL CONDENSATE REMOVAL PROCESS

Condensate Removal Process:

Details the step-by-step process for removing condensate from the unit.

B-Heating Start-Up

How To Operate Gas Valve (Figure 43)

Provides instructions on how to operate the gas valve for startup.

E-Testing Gas Supply Pressure

G- Proper Gas Flow (Approximate)

V-TYPICAL OPERATING CHARACTERISTICS

B-Cleaning Heat Exchanger and Burners

BURNER ACCESS/REMOVAL

VII-WIRING DIAGRAM, SEQUENCE OF OPERATION &TROUBLESHOOTING

A-Field Wiring, Thermostat Connections

Illustrates typical field wiring and thermostat connections for G26 units.

HEATING SEQUENCE OF OPERATION SURELIGHT CONTROL

HEATING SEQUENCE CONTINUED

NORMAL HEATING MODE

Continues the normal heating sequence flowchart.

ABNORMAL HEATING MODE

Continues the abnormal heating sequence flowchart with fault conditions.

COOLING SEQUENCE OF OPERATION SURELIGHT CONTROL

NORMAL COOLING MODE

Flowchart outlining the normal cooling sequence.

ABNORMAL COOLING MODE

Flowchart outlining abnormal cooling modes and troubleshooting.

CONTINUOUS LOW SPEED FAN SEQUENCE OF OPERATION SURELIGHT CONTROL

C-Heating Sequence of Operation

Details the heating sequence steps for the SureLight control.

D- SureLight Control Trouble Shooting Guide

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

Troubleshooting guide for units failing to operate in various modes.

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

PROBLEM 2: UNIT FAILS TO OPERATE IN THE COOLING OR HEATING MODE...

Troubleshooting steps for units where the combustion air blower operates but the unit fails.

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

Troubleshooting steps when the combustion air blower does not start during heating.

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

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

Troubleshooting steps when the combustion air blower runs but the ignitor does not.

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

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

Troubleshooting steps for premature burner shutdown or failure to stay lit.

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

PROBLEM 6.4

Troubleshooting for rough burner ignition and nuisance flame failures.

PROBLEM 7: CONTROL SIGNALS LOW FLAME SENSE DURING HEATING MODE

Troubleshooting steps for low flame sense signals.

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

Troubleshooting steps for indoor blower failure.

F-BCC2 Blower Control -1 and -2 Models

BCC2 TROUBLESHOOTING FLOWCHART

Troubleshooting flowchart for the BCC2 blower control.

G-G77 Ignition Control -1 and -2 Models

G776 IGNITION CONTROL TROUBLESHOOTING

Troubleshooting guide for the G776 ignition control when spark is present but pilot will not light.

G776 IGNITION CONTROL TROUBLESHOOTING

No spark and system will not work

Troubleshooting steps when no spark is present and the system does not work.

Pilot lights but main valve will not come on

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