EasyManua.ls Logo

Lennox G50UHX Series - User Manual

Lennox G50UHX Series
43 pages
Save Page as PDF
Print Icon
To Next Page IconTo Next Page
To Next Page IconTo Next Page
Loading...
Page 1
© 2000 Lennox Industries Inc.
Corp. 0005−L3
G50UH(X)
Service Literature
Revised 09−2006
G50UH(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. G50UH(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. G50UH(X) mod-
el units are equipped with the Lennox SureLight silicon ni-
tride ignition system. The G50UH(X) 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 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 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
High Altitude Page 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Parts Identification Page 16. . . . . . . . . . . . . . . . . . . . . . . .
I Unit Components Page 18. . . . . . . . . . . . . . . . . . . . . . .
II Installation Page 27. . . . . . . . . . . . . . . . . . . . . . . . . . . .
III Start Up Page 27. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IV Heating System Service Checks Page 27. . . . . . . . .
V Typical Operating Characteristics Page 29. . . . . . . . .
VI Maintenance Page 30. . . . . . . . . . . . . . . . . . . . . . . . . .
VII Wiring and Sequence of Operation Page 32. . . . . .
VIII SureLight Troubleshooting Guide Page 38. . . . . . .
IMPORTANT
Improper installation, adjustment, alteration, ser-
vice or maintenance can cause property damage,
personal 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.

Table of Contents

Questions and Answers

  • L
    Lisa BurkeAug 17, 2025
    How to fix Lennox G50UHX Furnace when indoor blower fails in cooling, heating, or continuous fan mode?
    • K
      Kelly FieldsAug 17, 2025
      If the indoor blower in your Lennox furnace isn't working in cooling, heating, or continuous fan mode, try the following: 1. Check the wiring and connections at the control and indoor blower motor, correcting any miswiring or loose connections. 2. Verify that 120V is being supplied to the indoor air blower by individually energizing "Y", "G", and "W" on the low voltage terminal strip. Note that when "W" is energized, the blower has a 45-second delay. If there is 120V to each motor tap but the blower does not operate, replace the motor. 3. If there is not 120V when "Y", "G", or "W" is energized, replace the control board. 4. Replace the run capacitor.
  • R
    Robert MeadowsAug 21, 2025
    Why Lennox Furnace combustion air blower energizes but the ignitor is not energized?
    • T
      Tonya HammondAug 21, 2025
      If your Lennox furnace's combustion air blower turns on but the ignitor doesn't, it could be due to: * Incorrect routing of the pressure switch lines. Ensure these lines are correctly routed. * Obstructions in the pressure lines, so remove any obstructions from the pressure lines and/or taps. * A low differential pressure across the pressure switch. Check the differential pressure, ensuring it exceeds the set point listed on the switch. Also, inspect for a restricted inlet vent and remove any blockage. Check for proper vent sizing and run length.
  • A
    aaronblackburnAug 25, 2025
    What to do if Lennox G50UHX Furnace fails to fire, and combustion air blower doesn't energize?
    • J
      jimmycampbellAug 25, 2025
      If your Lennox furnace fails to ignite and the combustion air blower isn't starting, it might be due to: * An open primary or secondary limit. Check the continuity across the switch(es), which reset automatically upon cool down. Also, check for any restrictions on the blower inlet air (including the filter) and outlet air. Determine the cause for limit activation before restarting the unit. * Incorrect wiring or loose connections at the limit switch(es). Inspect for correct wiring and secure connections, correcting any issues found.
  • R
    ronnie25Aug 27, 2025
    Why Lennox G50UHX Furnace fails to fire in heating mode and combustion air inducer doesn't energize?
    • M
      Mark PalmerAug 27, 2025
      If your Lennox furnace isn't firing and the combustion air inducer isn't starting, consider these possibilities: * Incorrect wiring or loose connections to the combustion air inducer. Check for correct wiring and secure connections, correcting any issues. * A prove switch stuck closed. Verify that the pressure switch is open when the combustion air inducer is not operating. Replace the switch if it's defective.
  • T
    Taylor HicksAug 30, 2025
    What causes Lennox G50UHX to signal low flame sense during heating mode?
    • J
      John HawkinsAug 30, 2025
      A low flame sense signal during heating mode in your Lennox furnace can be caused by: * An improperly located sense rod on the burner. Check the sense rod's position and properly locate it or replace it if it cannot be correctly positioned. * A contaminated sense rod. Inspect the sense rod for contamination or a coated surface. Clean the sense rod with steel wool or replace the sensor. Do not use sandpaper.
  • S
    Susan CohenSep 3, 2025
    Why does my Lennox Furnace light but shuts down prematurely?
    • J
      James JohnsonSep 3, 2025
      If your Lennox furnace burners light but the unit shuts down too soon, it could be due to low pressure differential at the prove switch. Check for a restricted exhaust vent and remove any blockage. Check for proper vent sizing.
  • C
    Christian LeSep 6, 2025
    What to do if Lennox G50UHX Furnace fails in cooling or heating mode, but combustion air inducer operates continuously?
    • E
      Elaine HatfieldSep 6, 2025
      If your Lennox furnace isn't working in cooling or heating mode, but the combustion air inducer runs continuously, check for: * An open ignitor circuit. Look for correct wiring and secure connections in the ignitor circuit. Also, check the multi-plug connections for correct installation. * A broken or failed ignitor. Unplug the ignitor and measure the resistance across it. If the resistance isn't between 10.9 and 19.7 ohms, replace the ignitor.
  • J
    Joseph ReeseSep 10, 2025
    Why Lennox G50UHX combustion air inducer does not energize on initial power-up?
    • T
      trogersSep 10, 2025
      If the combustion air inducer on your Lennox furnace doesn't start when you first turn it on, it could be due to: * An open combustion air inducer motor circuit. Check for 120V to the combustion air inducer. If there's no power, check the wire and connections. * A failed combustion air inducer motor. If power is present at the blower, replace the blower.
  • R
    Ricardo SanchezNov 13, 2025
    What to do if my Lennox G50UHX Furnace fails to operate in cooling, heating, or continuous fan mode?
    • M
      melissa20Nov 13, 2025
      If your Lennox Furnace isn't working in cooling, heating, or continuous fan mode, here's what you can check: * First, ensure the unit is receiving 120V main voltage and address any power failure issues. * Second, inspect the furnace wiring and connections, paying special attention to the 120V power to the make-up box and transformer, as well as the 24V wiring to the control board. * Third, examine the circuit breaker. If it trips immediately after being reset, replace it. If it continues to trip, look for a short circuit. * Fourth, verify the door interlock switch is activated when the door is closed, check wire connections to the switch, and test the switch's continuity in the closed position. * Fifth, confirm that the transformer output is 24V. Replace the transformer if it's ...

Summary

SPECIFICATIONS

Gas Heating Performance

Details input, output, AFUE, and seasonal efficiency for various models.

Indoor Blower

Specifies blower wheel diameter, motor output, and cooling capacity.

BLOWER DATA

HIGH ALTITUDE

PARTS IDENTIFICATION

G50 UH(X) PARTS ARRANGEMENT (UP FLOW POSITION)

Diagram showing the layout of major components in the up-flow configuration.

G50 UH (X) HEATING COMPONENTS

Exploded view illustrating key heating system components.

UNIT COMPONENTS

SureLight Integrated Ignition Control

Covers the SureLight ignition system, including control board, sensors, and ignitor.

IGNITOR AND SENSORS

Flame Sensor

Describes the flame sensor's function and location for sensing burner flame.

Ignitor

Blower Motors and Capacitors

COMBUSTION AIR INDUCER AND APPLICATIONS

Combustion Air Inducer (B6)

LIMIT CONTROLS

Flame Rollout Switches (S47)

Primary Limit Control (S10)

Secondary Limit Controls (S21)

GAS VALVE AND PROVING SWITCH

Gas Valve

Combustion Air Inducer Proving Switch (S18)

START-UP

Heating Start-Up

Step-by-step guide for initiating the furnace's heating operation.

SERVICE CHECKS

Testing Gas Supply Pressure

Proper Gas Flow & Combustion

OPERATING CHARACTERISTICS

Blower Operation and Adjustment

Temperature Rise

MAINTENANCE

Heat Exchanger and Burners

Procedure for cleaning the heat exchanger and burners to ensure proper operation.

WIRING AND SEQUENCE OF OPERATION

SURELIGHT CONTROL HEATING SEQUENCE OF OPERATION

SURELIGHT CONTROL COOLING SEQUENCE OF OPERATION

SURELIGHT CONTROL CONTINUOUS FAN SEQUENCE OF OPERATION

TROUBLESHOOTING GUIDE

Lennox G50UHX Series Specifications

General IconGeneral
ModelG50UHX Series
TypeGas Furnace
Efficiency RatingUp to 80% AFUE
Blower TypeMulti-speed
Vent TypeNatural Draft
StagesSingle-stage
Cabinet TypeInsulated
AFUE Rating80%
Blower Motor TypePSC
Heat Exchanger MaterialAluminized Steel
Heating Capacity44, 000-132, 000 BTU/h
DimensionsVaries by model
Fuel TypeNatural Gas or Propane
Blower MotorPSC
Filter Type1 inch
WarrantyLimited Lifetime Heat Exchanger warranty, 5-Year Limited Parts Warranty

Related product manuals