Lennox G26Q3/4-100 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 G26Q3/4-100 Specifications

General

Model	G26Q3/4-100
Type	Gas Furnace
Efficiency	80% AFUE
Heating Capacity	100, 000 BTU/h
Blower Type	Multi-speed
Fuel Type	Natural Gas
Input BTU	100, 000 BTU/h
Output BTU	80, 000 BTU/h
Stages	Single Stage
Blower Motor	PSC
Vent Size	4"
Filter Size	16" x 25" x 1"
Warranty	5-Year Limited Warranty on Parts

Summary

SPECIFICATIONS

Model Specifications (G26Q2-50 to G26Q4/5-75)

Technical specifications for G26 furnace models, including capacities, efficiencies, and dimensions.

Model Specifications (G26Q3/4-100 to G26Q4/5-125)

Technical specifications for larger G26 furnace models, detailing capacities and electrical data.

BLOWER PERFORMANCE DATA

VENTING TABLES

MINIMUM VENT PIPE DIAMETER REQUIRED

UNIT COMPONENTS

SURELIGHT CONTROL BOARD

TABLE 1 TERMINAL DESIGNATIONS

TABLE 2 DIAGNOSTIC CODES

Diagnostic codes for the SureLight control board, with LED indicators and meanings.

ELECTROSTATIC DISCHARGE (ESD) Precautions

BLOWER CONTROL

Diagnostic LED

TABLE 7 Furnace Control A3 Diagnostic LED

Table showing diagnostic LED states, meanings, and remedies.

TABLE 8 BLOWER CONTROL A15 TERMINAL DESIGNATIONS

BURNER ORIENTATION AND GAS VALVE

PRESSURE SWITCH OPERATION

15-Differential Pressure Switch (S64)

Explanation of the differential pressure switch and its function.

PRESSURE SWITCH MEASUREMENT

Measuring pressure differential

▲ WARNING SAFETY

Safety warning regarding bypassing safety systems.

INSTALLATION AND REPLACEMENT

Piping Installation

CONDENSATE REMOVAL PROCESS

III-START-UP

Heating Start-Up

How To Operate Gas Valve (Figure 43)

▲ WARNING UNDERWATER PARTS

Safety warning about operating the furnace if parts have been underwater.

HEATING SYSTEM SERVICE CHECKS

Testing Gas Supply Pressure

F-Check Manifold Pressure

▲ IMPORTANT MANOMETER

Important safety note regarding manometer connections and shut-off valves.

MANIFOLD CHECK

I-Flame Signal

TYPICAL OPERATING CHARACTERISTICS

BLOWER SPEED TAP SELECTION

TABLE 12 BLOWER SPEED CHART

VI-MAINTENANCE

Section on routine maintenance procedures for the furnace.

Cleaning Heat Exchanger and Burners

WIRING DIAGRAMS AND THERMOSTAT CONNECTIONS

A-Field Wiring, Thermostat Connections

Diagram showing typical field wiring and thermostat connections for G26 models.

Wiring Diagram G26 (-3 & -4 Shown)

KEY TO WIRING DIAGRAM

E-G26-1 and -2 Models Wiring

HEATING SEQUENCE OF OPERATION

NORMAL HEATING MODE

Flowchart detailing the normal heating mode sequence of operation.

ABNORMAL HEATING MODE

Flowchart detailing abnormal heating mode sequences and troubleshooting indicators.

HEATING SEQUENCE CONTINUED

NORMAL HEATING MODE CONTINUED

Continuation of the normal heating mode sequence of operation.

ABNORMAL HEATING MODE CONTINUED

Continuation of abnormal heating mode sequences and troubleshooting indicators.

COOLING SEQUENCE OF OPERATION

NORMAL COOLING MODE

Flowchart detailing the normal cooling mode sequence of operation.

ABNORMAL COOLING MODE

Flowchart detailing abnormal cooling mode sequences and troubleshooting indicators.

CONTINUOUS LOW SPEED FAN SEQUENCE

C-Heating Sequence of Operation

SureLight Control Trouble Shooting Guide

PROBLEM 1: UNIT FAILS TO OPERATE

Troubleshooting guide for units failing to operate in any mode.

1.1 - Diagnostic lights fail to light up

Troubleshooting steps when both diagnostic lights are off.

PROBLEM 1: UNIT FAILS TO OPERATE (CONT.)

1.5 - Combustion air blower remains energized

Troubleshooting steps when combustion air blower remains energized on startup.

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

Troubleshooting for units operating in cooling but not heating.

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

3.3 - Combustion air blower does not start

Troubleshooting combustion air blower not starting in heating mode.

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

Troubleshooting when combustion air blower runs but ignitor does not energize.

PROBLEM 5: UNIT FAILS TO FIRE IN HEATING MODE, IGNITOR ENERGIZED, UNIT FAILS TO LIGHT

5.1 - Ignitor energized, unit fails to light

Troubleshooting when ignitor is energized but unit fails to light.

PROBLEM 6: BURNERS LIGHT BUT SHUT DOWN PREMATURELY

Troubleshooting when burners light but shut off prematurely.

PROBLEM 6: BURNERS LIGHT BUT SHUT DOWN PREMATURELY (CONT.)

6.3 - Roll-out switch trips during heating demand

Troubleshooting when burners light but unit shuts down due to roll-out failure.

6.5 - Flame failure diagnostic lights

6.4 - Burners light roughly, unit fails to stay lit

Troubleshooting when burners light roughly and unit fails to stay lit.

PROBLEM 7: LOW FLAME SENSE

G26-1 and -2 Models Wiring and Sequence

BLOWER SPEED CHART

Heating Sequence of Operation

BCC2 Blower Control Troubleshooting

BCC2 TROUBLESHOOTING FLOWCHART

Troubleshooting flowchart for the BCC2 blower control.

FIGURE 55 BCC2 FLOWCHART

G776 IGNITION CONTROL TROUBLESHOOTING

Spark is present but pilot will not light

Troubleshooting guide for G776 ignition control when pilot will not light.

No spark and system will not work

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

Pilot lights but main valve will not come on

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

FIGURE 56 PILOT TROUBLESHOOTING

FIGURE 57 NO SPARK FLOWCHART

FIGURE 58 MAIN VALVE TROUBLESHOOTING