Lennox 80UHG4X-75

Page 1
 1999 Lennox Industries Inc.
Litho U.S.A.
Corp. 9728−L12
80UHG
Service Literature
Revised 01−2002
80UHG series units are mid−efficiency gas furnaces used
for upflow or horizontal applications only, manufactured
with tubular heat exchangers formed of aluminized steel.
80UHG units are available in heating capacities of 45,000
to 120,000 Btuh and cooling applications up to 5 tons. Refer
to Engineering Handbook for proper sizing.
Units are factory equipped for use with natural gas. Kits are
available for conversion to LPG operation. 80UHG−1 model
units use electronic (direct spark) ignition. 80UHG−2 and −3
model units are equipped with the Lennox SureLight silicon
nitride ignition system. The 80UHGX unit meets the Califor
nia Nitrogen Oxides (NO
x
) Standards and California Sea
sonal Efficiency requirements. All units use a redundant gas
valve to assure safety shut−off as required by A.G.A. or
C.G.A. Units may be installed in upflow or horizontal posi
tion.
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
Introduction 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Specifications 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Blower Data 3−4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
High Altitude 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Parts Identification 5−6. . . . . . . . . . . . . . . . . . . . . . . . . . . .
I Unit Components 6−15. . . . . . . . . . . . . . . . . . . . . . . . . . .
II Installation 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
III Start Up 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IV Heating System Service Checks 16−17. . . . . . . . . . .
V Typical Operating Characteristics 18. . . . . . . . . . . . . .
VI Maintenance 19−20. . . . . . . . . . . . . . . . . . . . . . . . . . . .
VII Wiring and Sequence of Operation 21−28. . . . . . . . .
VIII SureLight Troubleshooting Guide 29−34. . . . . . . . . .

Lennox 80UHG4X-75 Specifications

General

Model	80UHG4X-75
Category	Furnace
Heating Capacity	75, 000 BTU/h
Efficiency Rating	80%
AFUE	80%
Fuel Type	Natural Gas
Blower Type	Multi-speed
Stages	Single Stage
Blower Motor Type	PSC
Filter Type	Standard

Summary

Introduction to 80 UHG Series Units

Unit Specifications

Optional Accessories

Lists optional accessories available for the 80UHG series units.

Blower Performance and Data

Filter Air Resistance

Details air resistance values for different airflow rates.

High Altitude Derate

Provides pressure settings for high altitude installations.

Unit Components and Identification

Parts Identification

Illustrates the external parts of the 80UHG furnace.

I-Unit Components

Details major internal components of the 80UHG unit.

Safety Precautions

Covers ESD precautions and shock hazard warnings.

Furnace Control Systems

SureLight Control (80 UHG-2, -3)

Details the SureLight control and its electronic ignition.

Fan Time Control

Explains fan operation timing adjustments.

Diagnostic Codes and Ignition Sequence

SureLight Diagnostic Codes

Lists LED codes for troubleshooting the SureLight control board.

SureLight Ignition Sequence

Details the step-by-step ignition process for the SureLight system.

SureLight Control Board and Ignitor

Control Board Terminals

Diagram and terminal designations for the SureLight control board.

Flame Sensor Operation

Explains the function and placement of the flame sensor.

80 UHG-1 Furnace Control (EGC-2)

EGC-2 Ignition Control

Describes the EGC-2 ignition control and its operation.

Blower and Fan Timings

Explains blower operation and fan off timing adjustments.

EGC-2 Control and Troubleshooting

Thermostat Connection

How to connect the thermostat to the EGC-2 control board.

EGC-2 Diagnostic Codes

Lists LED diagnostic codes for the EGC-2 control board.

Major Unit Components

Blower Motors and Capacitors

Details blower motor specifications and capacitor ratings.

Combustion Air Inducer and Rollout Switches

Explains inducer function and safety switch locations.

Safety Controls and Gas Valve

Limit Controls

Explains the function of primary and secondary limit controls.

Ignition Components and Gas Valve

Details spark electrode, flame sensor, and gas valve.

Burner Assembly and Airflow Sensing

Burner and Electrode Orientation

Illustrates burner layout and gap specifications for ignition.

Combustion Air Blower Prove Switch

Explains the function and operation of the combustion air blower prove switch.

Installation and Start-Up Procedures

Placement and Installation

Guidelines for installing the unit according to codes.

Heating Start-Up and Shutdown

Procedures for starting the furnace and safe shutdown.

Heating System Service Checks

Gas Piping and Pressure Testing

Covers gas piping requirements, testing, and pressure checks.

Manifold Pressure Adjustment

Details how to check and adjust manifold pressure.

Gas Flow and Flame Signal Measurement

Manifold Adjustment and Gas Flow

Procedures for manifold adjustment and checking gas flow.

Flame Signal Measurement

How to measure the flame signal using a microamp meter.

Typical Operating Characteristics

Blower Operation and Adjustment

Explains blower operation, adjustment, and speed settings.

Temperature Rise and Static Pressure

Details how to measure temperature rise and external static pressure.

Blower Speed Taps and Maintenance

Blower Speed Taps (Leaded Motors)

How to select blower speed taps for 80UHG-2 models.

Maintenance Procedures

Routine checks and cleaning for filters, heat exchangers, and burners.

Unit Maintenance Checks

Blower, Flue, and Electrical Checks

Inspecting blower, flue, chimney, wiring, voltage, and motor amp-draw.

Wiring and Sequence of Operation

80 UHG-1 Wiring and EGC Control Sequence

Wiring details and operational sequence for 80UHG-1 with EGC control.

Heating Sequence of Operation

Cooling and Continuous Fan Sequences

80 UHG-2 SureLight Control Sequence

Heating Sequence of Operation (Continued)

Heating Sequence of Operation (Continued)

Cooling Sequence of Operation

Continuous Heat Fan Sequence

Troubleshooting SureLight Control

Troubleshooting Guide

Guide to diagnose and fix common operational failures.

Troubleshooting Unit Failures

Unit Fails to Operate

Diagnosing issues when the unit fails to operate in any mode.

Unit Fails to Fire (No Inducer)

Troubleshooting when the inducer does not start during heating.

Troubleshooting Ignition Failures

No Combustion Air Inducer (No Fire)

Diagnosing why the inducer won't start with heating demand.

Ignitor Not Energized

Addressing issues when the inducer runs but the ignitor does not.

Troubleshooting Ignition and Burner Issues

Ignitor Energized, Unit Fails to Light

Actions when the ignitor is energized but the unit does not fire.

Burners Light, Then Shut Down Prematurely

Diagnosing why burners light but then shut off unexpectedly.

Troubleshooting Premature Shutdowns

Burners Light, Unit Shuts Down Prematurely (Cont.)

Continued troubleshooting for premature burner shutdowns.

Advanced Troubleshooting Conditions

Low Flame Sense Issues

Resolving diagnostic codes for low flame sense.

Indoor Blower Operation Failures

Addressing problems with the indoor blower not operating.