Lennox G26Q3-75 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 G26Q3-75 Specifications

General

Model	G26Q3-75
Category	Furnace
Fuel Type	Natural Gas
Efficiency	80% AFUE
Heating Capacity	75, 000 BTU/h
Blower Motor	Multi-Speed
Ignition System	Direct Spark Ignition
Blower Motor Type	PSC
Warranty	Limited Lifetime Heat Exchanger, 5-Year Parts
Stages	Single Stage
Ignition Type	Direct Spark Ignition

Summary

G26 SERIES UNITS

SPECIFICATIONS

Optional Accessories

BLOWER PERFORMANCE DATA

INTAKE and EXHAUST PIPE VENTING TABLE

GAS PIPE CAPACITY

Table showing gas pipe capacity in cubic feet per hour (kL/hr) based on pipe size and length.

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

DIAGNOSTIC CODES

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

II-PLACEMENT AND INSTALLATION

A-PVC Joint Cementing Procedure

Step-by-step instructions for properly joining PVC pipes using solvent cement and primer.

B-Venting Considerations

Important factors to consider when installing vent pipes, including common venting and pipe thickness.

Intake Piping

Exhaust Piping

Instructions for installing exhaust piping, including slope requirements and support spacing.

Removal of Unit from Common Venting System

Intake and Exhaust Piping Terminations

Guidelines for terminating intake and exhaust pipes horizontally or vertically, with figures showing typical configurations.

III-START-UP

A-Preliminary and Seasonal Checks

Initial checks to perform before starting the furnace, including electrical wiring and condensate traps.

IV-HEATING SYSTEM SERVICE CHECKS

B-Exhaust CO2 and CO content

Guidelines for checking exhaust CO2 and CO content to ensure proper combustion and safety.

C-Gas Piping

D-Testing Gas Piping

E-Testing Gas Supply Pressure

F-Check Manifold Pressure

Instructions for checking manifold pressure on natural gas and LP/propane units.

V-TYPICAL OPERATING CHARACTERISTICS

A-Blower Operation and Adjustment

B-Temperature Rise

C-External Static Pressure

D-Blower Speed Taps Leadless Motors (-1, -2, -3 and -4 Models)

VI-MAINTENANCE

A-Filters

B-Cleaning Heat Exchanger and Burners

Cleaning the Burner Assembly

SIMPLIFIED BURNER REMOVAL

VII-WIRING DIAGRAM, SEQUENCE OF OPERATION &TROUBLESHOOTING

A-Field Wiring, Thermostat Connections

Diagram showing typical field wiring for G26 units, including thermostat connections.

B-Wiring Diagram G26 (-3 & -4 Shown)

HEATING SEQUENCE OF OPERATION SURELIGHT CONTROL

COOLING SEQUENCE OF OPERATION SURELIGHT CONTROL

CONTINUOUS LOW SPEED FAN SEQUENCE OF OPERATION SURELIGHT CONTROL

C-Heating Sequence of Operation

Step-by-step description of the SureLight control's heating sequence from call for heat to satisfied demand.

D- SureLight Control Trouble Shooting Guide

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

Troubleshooting steps for common issues where the unit fails to operate in any mode.

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

PROBLEM 3: UNIT FAILS TO FIRE IN THE HEATING MODE...

PROBLEM 4: UNIT FAILS TO FIRE IN THE HEATING MODE...

PROBLEM 5: UNIT FAILS TO FIRE IN THE HEATING MODE...

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

PROBLEM 7: CONTROL SIGNALS LOW FLAME SENSE...

PROBLEM 8: INDOOR BLOWER FAILS TO OPERATE...

PROBLEM 9: RF STATIC DURING TIME FOR IGNITION

F-BCC2 Blower Control -1 and -2 Models

G-G776 Ignition Control -1 and -2 Models

G776 IGNITION CONTROL TROUBLESHOOTING -1 and -2 MODELS