Lennox G40UH(X)

Page 1
© 2000 Lennox Industries Inc.
G40UH(X)
Service Literature
Corp. 0006−L3
Revised 09−2006
G40UH(X) series units are mid−efficiency gas furnaces
used for upflow or horizontal applications only, manufac-
tured with Lennox Duralok Plus heat exchangers formed of
aluminized steel. G40UH(X) units are available in heating
capacities of 44,000 to 154,000 Btuh and cooling applica-
tions up to 5 tons. Refer to Engineering Handbook for prop-
er sizing.
Units are factory equipped for use with natural gas. Kits are
available for conversion to LPG operation. G40UH(X) model
units are equipped with a hot surface ignition system. The
G40UH(X) unit meets the California Nitrogen Oxides (NO
x
)
Standards and California Seasonal Efficiency requirements.
All units use a redundant gas valve to assure safety shut−off
as required by C.S.A.
All specifications in this manual are subject to change. Pro-
cedures outlined in this manual are presented as a recom-
mendation only and do not supersede 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 and do not constitute
code.
TABLE OF CONTENTS
Specifications Page 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Blower Data Page 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
High Altitude Page 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Parts Identification Page 14. . . . . . . . . . . . . . . . . . . . . . . .
I Unit Components Page 16. . . . . . . . . . . . . . . . . . . . . . .
II Installation Page 24. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
III Start Up Page 24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IV Heating System Service Checks Page 24. . . . . . . . .
V Typical Operating Characteristics Page 28. . . . . . . . .
VI Maintenance Page 28. . . . . . . . . . . . . . . . . . . . . . . . . .
VII Wiring and Sequence of Operation Page 30. . . . . .
VIII SureLight Troubleshooting Guide Page 41. . . . . . .
IMPORTANT
Improper installation, adjustment, alteration, service
or maintenance can cause property damage, person-
al injury or loss of life. Installation and service must
be performed by a qualified installer, service agency
or the gas supplier.
WARNING
Electric shock hazard. Can cause injury
or death. Before attempting to perform
any service or maintenance, turn the
electrical power to unit OFF at discon-
nect switch(es). Unit may have multiple
power supplies.
WARNING
Sharp edges.
Be careful when servicing unit to avoid sharp edges
which may result in personal injury.

Lennox G40UH(X) Specifications

General

Brand	Lennox
Model	G40UH(X)
Category	Furnace
Language	English

Summary

I-UNIT COMPONENTS

Control Transformer (T1)

Transformer providing low voltage power to the unit.

Door Interlock Switch (S51)

Safety switch that shuts off unit when blower door is removed.

SureLight Integrated Ignition Control (A92)

Controls furnace ignition, operations, and features diagnostic LEDs.

Combustion Air Inducer (B6)

Horizontal Applications

How the furnace can be installed in horizontal configurations.

Flame Rollout Switches (S47)

Blower Motors and Capacitors

Details on direct drive blower motors and capacitors.

Primary Limit Control (S10)

Control that prevents operation during excess heat in the vestibule.

Secondary Limit Controls (S21)

Controls that prevent operation during excess heat in the blower compartment.

Gas Valve

Gas Valve Operation

Details on the gas valve and its function.

Combustion Air Inducer Proving Switch (S18)

Monitors inducer operation and prevents burner operation if blocked.

III-START-UP

Preliminary and Seasonal Checks

Pre-start checks and seasonal maintenance procedures.

Heating Start-Up

Steps for safely initiating furnace heating operation.

IV-HEATING SYSTEM SERVICE CHECKS

Gas Piping

Guidelines for gas piping installation and checks.

Testing Gas Supply Pressure

How to test gas supply pressure and manifold pressure.

Proper Gas Flow & Combustion

Checking gas flow and combustion parameters.

V-TYPICAL OPERATING CHARACTERISTICS

Blower Operation and Adjustment

How the blower operates and how to adjust its speed.

Temperature Rise

How to measure and set the correct temperature rise.

External Static Pressure

Procedure for measuring external static pressure.

VI-MAINTENANCE

Filters

Instructions for inspecting, cleaning, or replacing air filters.

Heat Exchanger and Burners

Procedure for cleaning heat exchangers and burners.

Blower Speed Taps

How to adjust blower speeds.

Supply Air Blower

Maintenance for the supply air blower.

Flue and Chimney

Inspection and maintenance of flue and chimney systems.

Electrical

Checks for wiring connections, voltage, and motor amp-draw.

VII- Wiring and Sequence of Operation

Sequence of Operation

Describes the step-by-step process for heating and cooling cycles.

HEATING SEQUENCE OF OPERATION

COOLING SEQUENCE OF OPERATION

CONTINUOUS HEAT SPEED FAN SEQUENCE OF OPERATION

TROUBLE SHOOTING GUIDE

Unit Fails to Operate

Troubleshooting steps when the unit fails in any mode.

Unit Fails to Fire

Diagnosing issues when the unit fails to ignite or start.

Burners Light Prematurely

Troubleshooting when burners light but shut down unexpectedly.