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Lennox ML193UH090P36C - User Manual

Lennox ML193UH090P36C
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Page 1
© 2014 Lennox Industries Inc.
Litho U.S.A.
Corp. 1025-L5
ML193UH
Service Literature
Revised 03-2014
ML193UH SERIES UNITS
ML193UH series units are high-efficiency gas furnaces
manufactured with Lennox DuralokPlust aluminized steel
clamshell-type heat exchangers, with a stainless steel con
densing coil. ML193UH units are available in heating input
capacities of 44,000 to 132,000 Btuh (13 to 38.6 kW) and
cooling applications from 2 through 5 tons (7.0 through
17.6 kW). Refer to Engineering Handbook for proper siz
ing.
Units are factory equipped for use with natural gas. A kit is
available for conversion to LPG operation. All ML193UH
units are equipped with a hot surface ignition system. The
gas valve is redundant to assure safety shut-off as required
by C.S.A.
The heat exchanger, burners and manifold assembly can
be removed for inspection and service. The maintenance
section gives a detailed description on how this is done.
All specifications are subject to change. Procedures out
lined in this manual are presented as a recommendation
only and do not supersede or replace local or state codes.
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.
Table of Contents
Specifications 2.................................
Optional Accessories 3..........................
Blower Performance Data 4......................
I-Unit Components 7............................
II Placement and Installation 19....................
III-Start-Up 40...................................
IV-Heating System Service Checks 41..............
V-Typical Operating Conditions 43.................
VI-Maintenance 44...............................
VII-Sequence of Operation and Flow Charts 47......
WARNING
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 licensed professional HVAC in
staller (or equivalent), service agency or the gas sup
plier.
WARNING
Sharp edges.
Be careful when servicing unit to avoid sharp edges
which may result in personal injury.

Table of Contents

Questions and Answers

  • A
    Alexis HopkinsAug 6, 2025
    What to do if Lennox Furnace fails to fire in the heating mode, combustion air inducer does not energize?
    • T
      Tom HughesAug 6, 2025
      If your Lennox furnace fails to fire and the combustion air inducer isn't energizing, check for correct wiring and secure connections to the combustion air inducer. Correct any wiring issues or replace loose connections. Also, verify that the pressure switch is open when the combustion air inducer is not operating; replace the switch if it's stuck closed.
  • O
    olsonmelissaAug 11, 2025
    What to do if my Lennox ML193UH090P36C Furnace unit fails to operate in cooling, heating, or continuous fan mode?
    • C
      Cindy MitchellAug 11, 2025
      If your Lennox furnace fails to operate, start by checking the 120V main voltage supply and address any power failures. Inspect the furnace wiring and connections, ensuring they are correctly wired to the power make-up box and transformer, and that the 24V wiring to the control is correct. Replace any blown fuses, and if they continue to blow, check for shorts. Verify that the door switch is activated when closed, check the wire connections, and test the switch's continuity; replace if defective. Confirm the transformer output is 24V, replacing it if faulty. If these steps don't resolve the issue, the control might be defective and require replacement.
  • J
    Jeremiah ChandlerAug 16, 2025
    Why Lennox Furnace indoor blower fails to operate in cooling, heating, or continuous fan mode?
    • B
      Brandon HillAug 16, 2025
      If the indoor blower in your Lennox furnace isn't working, first check the wiring and connections at the control and blower motor, correcting any miswiring or loose connections. Then, verify that 120V is supplied to the blower by individually energizing 'Y', 'G', and 'W' on the low voltage terminal strip. Remember that when 'W' is energized, the blower starts after a 45-second delay. If there's 120V to each motor tap but the blower remains inoperative, replace the motor. If there's no 120V when 'Y', 'G', or 'W' is energized, the control is likely defective and needs replacement. Finally, check and replace the run capacitor if it's defective.
  • M
    Mary Glover PhDAug 21, 2025
    What to do if Lennox Furnace burners light but unit shuts down prematurely?
    • H
      Hannah LeeAug 21, 2025
      If your Lennox furnace burners light but the unit shuts down too soon, check for a restricted intake or exhaust vent and remove any blockages. Ensure the correct concentric vent kit is installed. Also, inspect the condensate drain line for proper slope and any blockages, ensuring condensate flows freely during operation; repair or replace any improperly installed lines.
  • M
    Mrs. Phyllis Yang DDSAug 27, 2025
    What to do if Lennox Furnace fails to fire in heating mode, combustion air blower energizes, ignitor is energized?
    • W
      William WernerAug 27, 2025
      If your Lennox furnace isn't firing, but the combustion air blower and ignitor are working, check that gas is being supplied to the unit. Verify the line pressure at the gas valve, ensuring it doesn't exceed 13" WC for both natural and propane, and reads a minimum of 4.5" WC for natural and 11.0" WC for propane. Inspect the gas valve wiring and connections at multi-pin control amp plugs or the valve for correctness and tightness. If 24V is supplied to the gas valve approximately 35 seconds after heat demand but the valve doesn't open, replace the valve. If 24V is not supplied, replace the control.
  • J
    Jessica GarciaDec 1, 2025
    What to do if Lennox ML193UH090P36C Furnace fails to fire in the heating mode, combustion air inducer energizes, ignitor is not energized?
    • A
      Angela JenkinsDec 1, 2025
      If your Lennox furnace isn't firing, the combustion air inducer is working, but the ignitor isn't starting, ensure the pressure switch lines are correctly routed. Remove any obstructions from the pressure lines and/or taps. Check the pressure switch lines for leaks and replace any broken lines. Also, check for condensate in the pressure switch line and remove it. Verify the differential pressure across the pressure switch exceeds the set point listed on the switch, and check for a restricted inlet vent, removing any blockage and ensuring proper vent sizing and run length. Confirm that the proper pressure switch is installed; replace if necessary. Check the wiring and connections at the pressure switch for correctness and tightness. If all these checks pass, the pressure switch may be fault...

Summary

UNIT INFORMATION

ML193 UH Series Units Overview

General introduction to ML193UH series high-efficiency gas furnaces.

SPECIFICATIONS

OPTIONAL ACCESSORIES

Cabinet Accessories

Kits for horizontal suspension and return air bases.

GAS HEAT ACCESSORIES

Installation Clearances

Required spacing for safe installation of the furnace.

PARTS IDENTIFICATION

ML193 UH Furnace Components Diagram

Visual guide to the major parts of the ML193UH furnace.

I-UNIT COMPONENTS

Control Box Components

Details transformer, interlock switch, and integrated ignition control.

B-Heating Components

Ignitor and Flame Sensor

Components responsible for ignition and flame sensing.

II-PLACEMENT AND INSTALLATION

Pipe & Fittings Specifications

Standards and materials for vent and condensate piping.

Venting Practices

Piping Suspension and Wall Thickness Guidelines

Rules for supporting and installing vent pipes.

VENT TERMINATION CLEARANCES

Non-Direct Vent Clearances

Required distances for vent terminals and air inlets.

Details of Exhaust Piping Terminations for Non-Direct Vent Applications

Condensate Piping Installation

Steps for installing condensate traps and drain lines.

III-START-UP

Preliminary Checks and Heating Start-Up

Steps for initial unit setup and operation.

V-TYPICAL OPERATING CHARACTERISTICS

Blower Operation and Adjustment

How the blower functions and is adjusted for airflow.

VI-MAINTENANCE

Routine Maintenance Checks

Procedures for checking blower, filters, and piping.

VII-WIRING DIAGRAM AND SEQUENCE OF OPERATION

Heating Sequence of Operation (Control 100973)

Step-by-step process for heating mode operation.

COOLING SEQUENCE OF OPERATION

Cooling Mode Operation

Flowchart for cooling mode and abnormal conditions.

HEATING SEQUENCE OF OPERATION (Control 103085)

Lennox ML193UH090P36C Specifications

General IconGeneral
BrandLennox
ModelML193UH090P36C
CategoryFurnace
LanguageEnglish

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