Lennox 80MGF Series

Page 1
© 1998 Lennox Industries Inc.
Corp. 9801−L2
80MGF
Service Literature
Revised 08−2004
80MGF SERIES UNITS
80MGF series units are mid−efficiency gas furnaces
manufactured with tubular heat exchangers formed of alu-
minized or stainless steel. 80MGF units are available in
heating capacities of 45,000 to 140,000 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 conversion to LPG operation. All 80MGF units
built proir to September 98 use electronic (direct spark) igni-
tion. 80MGF−11 model units are equipped with the Lennox
SureLight ignition system. The 80MGFX unit meets the
California Nitrogen Oxides (NO
x
) Standards and California
Seasonal Efficiency requirements. All units use a redun-
dant gas valve to assure safety shut−off as required by
A.G.A. or C.G.A.
The heat exchanger, burners and manifold assembly can
easily be removed for inspection and service by simply dis-
connecting gas, unplugging wiring harness and spark wires
and removing four screws holding the heat exchanger in
place. Then the heat exchanger slides out of the cabinet.
All specifications in this manual are subject to change.
Procedures outlined in this manual are presented as a rec-
ommendation 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.
Units may be installed in upflow, downflow or horizontal
position. The heat exchanger is designed for upright or
horizontal use only. When the unit is installed in the down-
flow position, the heat exchanger is field removed and re-
installed so it is upright when the cabinet is inverted. No
field conversion is required when the unit is installed in the
horizontal position.
TABLE OF CONTENTS
Introduction 1. . . . . . . . . . . . . . . . . . . . . . . .
Specifications 2. . . . . . . . . . . . . . . . . . . . . .
Blower Data 5. . . . . . . . . . . . . . . . . . . . . . .
Parts Identification 7. . . . . . . . . . . . . . . . . .
I Unit Components 9. . . . . . . . . . . . . . . . . .
II Installation 19. . . . . . . . . . . . . . . . . . . . . . .
III Start Up 19. . . . . . . . . . . . . . . . . . . . . . . . .
Preliminary Seasonal Checks 20 . . . . .
Heating Start Up 20. . . . . . . . . . . . . . . .
IV Heating System Service Checks 20. . .
V Typical Operating Characteristics 22. . .
VI Maintenance 24. . . . . . . . . . . . . . . . . . . .
VII Wiring and Sequence of Operation 26.
VIII SureLight Control Troubleshooting 40.

Lennox 80MGF Series Specifications

General

Stages	Single-stage
Efficiency	80% AFUE
Blower Motor	Multi-speed
Ignition	Hot Surface Ignition
Cabinet Type	Upflow/Horizontal
Blower Type	Multi-Speed
Fuel Type	Natural Gas
Ignition Type	Hot Surface
Warranty	5-year parts warranty

Summary

80 MGF SERIES UNITS

BLOWER PERFORMANCE DATA

80 MGF2-45, 80 MGF2-60 AND 80 MGF2-75 BLOWER PERFORMANCE

Blower performance data for specific 80MGF models.

80 MGF3-60 AND 80 MGF3-75 BLOWER PERFORMANCE

Blower performance data for specific 80MGF models.

BLOWER PERFORMANCE DATA (continued)

80 MGF4-75, 80 MGF34-100 AND 80 MGF34-120 BLOWER PERFORMANCE

Blower performance data for specific 80MGF models.

80 MGF45-100, 80 MGF45-120 AND 80 MGF45-140 BLOWER PERFORMANCE

Blower performance data for specific 80MGF models.

FILTER AIR RESISTANCE

80 MGF PARTS IDENTIFICATION and ORIENTATION

HEATING COMPONENTS (shown in horizontal position)

Visual identification of heating components within the unit.

80 MGF BURNER ASSEMBLY (Shown With SureLight ignitor)

80 MGF BLOWER DOOR COMPONENTS - BLOWER ACCESS (SureLight MODEL SHOWN)

I-UNIT COMPONENTS

A-Blower Door Components (Figure 4)

Details on components located on the blower access door.

Blower Control and Timings

FURNACE CONTROL A3 TERMINAL DESIGNATIONS

4- EGC Control (A3)

Ignition Control

Explanation of the direct spark ignition sequence.

Safety Circuits

Overview of safety circuits and their functions.

Blower Operation Fan Off Timings

Details on blower operation and fan off-time adjustments.

Troubleshooting

6- SureLight Ignition System A3 (-11 models)

5-Flame Sensor (-11 models)

Description and function of the flame sensor.

6- SureLight Ignition System A3 (-11 models) (continued)

a-Electronic Ignition

Explanation of the SureLight electronic ignition process.

b-Fan Time Control

Details on fan time adjustments for the SureLight system.

Blower Motors and Capacitors

C-Combustion Air Blower (B6)

Information on the combustion air blower motor.

D-Flame Rollout Switches (S47)

Details on the function and operation of rollout switches.

E-Primary Limit Control (S10)

Explanation of the primary limit control.

Component Details

F-Secondary Limit Controls (S21)

Information on secondary limit controls.

G-Spark Electrode and Flame Sensor (Models with EGC or Ram control only)

Arrangement of spark electrode and flame sensor.

H-Gas Valve

Information on the gas valve, its types, and features.

II-PLACEMENT AND INSTALLATION

III-START-UP

IV-HEATING SYSTEM SERVICE CHECKS

A.G.A.C.G.A. Certification

Details on unit certifications and compliance.

B-Gas Piping

Guidelines for gas piping installation and requirements.

C-Testing Gas Piping

Procedures for testing gas piping integrity.

IV-HEATING SYSTEM SERVICE CHECKS (continued)

D-Testing Gas Supply Pressure

How to test gas supply pressure.

E-Check Manifold Pressure

Procedure for checking manifold pressure.

F- Proper Gas Flow (Approximate)

Method for checking gas flow rate.

IV-HEATING SYSTEM SERVICE CHECKS (continued)

G-High Altitude Derate

Information on derating for high altitude installations.

H-Flame Signal

How to measure the flame signal.

V-TYPICAL OPERATING CHARACTERISTICS

A-Blower Operation and Adjustment

General procedures for blower operation and adjustment.

B-Temperature Rise

Factors affecting and setting temperature rise.

V-TYPICAL OPERATING CHARACTERISTICS (continued)

C-External Static Pressure

How to measure and adjust external static pressure.

D-Blower Speed Taps Leadless Motors

Changing blower speed taps on leadless motors.

V-TYPICAL OPERATING CHARACTERISTICS (continued)

E-Blower Speed Taps Leaded Motors -11 Models

Changing blower speed taps on leaded motors.

VI-MAINTENANCE

Filters

Filter inspection, cleaning, and replacement guidelines.

A-Cleaning Heat Exchanger and Burners

Procedures for cleaning heat exchangers and burners.

B-Supply Air Blower

Maintenance for the supply air blower motor.

VI-MAINTENANCE (continued)

C-Flue and Chimney

Requirements for flue and chimney inspection.

D-Electrical

Electrical checks for connections, voltage, and amp-draw.

VII-WIRING AND SEQUENCE OF OPERATION

80 MGF WITH RAM CONTROL

Sequence of operation for units with RAM control.

80 MGF TROUBLESHOOTING SEQUENCE

80 MGF TROUBLESHOOTING SEQUENCE - COOLING

80 MGF TROUBLESHOOTING SEQUENCE - FAN ONLY

80 MGF WITH EGC-2 IGNITION CONTROL

1 - When disconnect is closed, 120 V is routed...

Sequence of operation with EGC-2 ignition control.

80 MGF WITH EGC-2 HEATING SEQUENCE OF OPERATION

80 MGF WITH EGC-2 COOLING SEQUENCE OF OPERATION

80 MGF WITH EGC-2 MANUAL CONTINUOUS FAN SEQUENCE OF OPERATION

80 MGF WITH EGC-1 IGNITION CONTROL

1 - When disconnect is closed, 120 V is routed...

Sequence of operation with EGC-1 ignition control.

80 MGF WITH EGC-1 HEATING SEQUENCE OF OPERATION

80 MGF WITH EGC-1 COOLING SEQUENCE OF OPERATION

80 MGF WITH EGC-1 MANUAL CONTINUOUS FAN SEQUENCE OF OPERATION

80 MGF WITH SURELIGHT IGNITION CONTROL

1- When there is a call for heat, W1 of the thermostat...

Sequence of operation with SureLight ignition control.

SURELIGHT CONTROL HEATING SEQUENCE OF OPERATION

SURELIGHT CONTROL COOLING SEQUENCE OF OPERATION

SURELIGHT CONTROL CONTINUOUS LOW SPEED FAN SEQUENCE OF OPERATION

VIII-Troubleshooting-SureLight Control

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

Troubleshooting unit failures in various operating modes.

VIII-Troubleshooting-SureLight Control (continued)

PROBLEM 2: UNIT FAILS TO OPERATE IN THE COOLING OR HEATING MODE, BUT COMBUS- TION AIR BLOWER OPERATES CONTINUOUS.

Troubleshooting issues with combustion air blower operation.

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

Troubleshooting failure of combustion air blower to start in heating mode.

VIII-Troubleshooting-SureLight Control (continued)

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

Further troubleshooting for combustion air blower failure.

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

Troubleshooting ignitor not energizing with combustion air blower active.

VIII-Troubleshooting-SureLight Control (continued)

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

Troubleshooting unit failure with energized ignitor.

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

Troubleshooting burners shutting down prematurely.

VIII-Troubleshooting-SureLight Control (continued)

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

Continued troubleshooting for premature burner shutdown.

VIII-Troubleshooting-SureLight Control (continued)

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

Continued troubleshooting for premature burner shutdown.

PROBLEM 7: CONTROL SIGNALS LOW FLAME SENSE DURING HEATING MODE

Troubleshooting low flame sense signal issues.

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

Troubleshooting indoor blower failure in all modes.

PROBLEM 9: RF STATIC DURING TIME FOR IGNITION

Troubleshooting RF static during ignition.

SERVICE NOTES