Lennox G50UHi Unit Information
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Lennox G50UHi Unit Information

Lennox G50UHi Unit Information

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See also: User's Information Manual
Service Literature
G50UHi series units are mid−efficiency gas furnaces used
for upflow or horizontal applications only, manufactured
®
with Lennox Duralok Plus
minized steel. G50UHi units are available in heating capac-
ities of 66,000 to 154,000 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. G50UHi model
units are equipped with the Lennox SureLight
tride ignition system and blower control module. The blower
control module allows the G50Ui to maintain a constant
CFM over a wide range of operating static pressure. All units
use a redundant gas valve to assure safety shut−off as re-
quired 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

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G50UHi Series Units
heat exchangers formed of alu-
®
silicon ni-
. . . . . . . . . . . . . .
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Corp. 0304−L4
Revised 10−2005
Improper installation, adjustment, alteration, service
1
or maintenance can cause property damage, person-
2
al injury or loss of life. Installation and service must
be performed by a qualified installer, service agency
3
or the gas supplier.
4
6
8
Electric shock hazard. Can cause injury
or death. Before attempting to perform
17
any service or maintenance, turn the
electrical power to unit OFF at discon-
17
nect switch(es). Unit may have multiple
17
power supplies.
20
20
Sharp edges.
22
Be careful when servicing unit to avoid sharp edges
which may result in personal injury.
28
Page 1
G50UHi
IMPORTANT
WARNING
WARNING
© 2003 Lennox Industries Inc.

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  • Page 1: Table Of Contents

    ® with Lennox Duralok Plus heat exchangers formed of alu- minized steel. G50UHi units are available in heating capac- ities of 66,000 to 154,000 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.

  • Page 2: Specifications

    SPECIFICATIONS Model No. G50UHi−36A−070 G50UHi−36B−090 G50UHi−48B−090 Heating Input − Btuh (kW) 66,000 (19.3) 88,000 (25.8) 88,000 (25.8) Performance Performance Output − Btuh (kW) 54,100 (15.8) 72,100 (21.1) 72,100 (21.1) AFUE 80.0% 80.0% 80.0% California Seasonal Efficiency 74.8% 75.7% 75.3% High static (CSA) − in. w.g. (Pa) .50 (124)

  • Page 3: High Altitude

    SPECIFICATIONS Model No. G50UHi−60C−110 G50UHi−60D−135 Heating Input − Btuh (kW) 110,000 (32.2) 132,000 (38.7) Performance Performance Output − Btuh (kW) 89,400 (26.2) 106,900 (31.3) AFUE 80.0% 80.0% California Seasonal Efficiency 73.9% 75.0% High static (CSA) − in. w.g. (Pa) .50 (124) .50 (124)

  • Page 4: Blower Data

    NOTE − Jumper selections are NOT NOTE Jumper selections are NOT printed on the Blower Control Module. Ramp Off, A, B, C Off, A, B, C G50UHi−36A−070 Jumper Speed Selector External Static Speed 1 Speed 2 Speed 3 Speed 4...
  • Page 5 G50UHi−48B−090 Jumper Speed Selector External External Speed 1 Speed 2 Speed 3 Speed 4 Speed 5 Speed 6 Speed 7 Static Factory Default Factory Default Factory Default Factory Default Pressure Cool Dehumid Heat in. w.g. Pa cfm L/s Watts cfm L/s...
  • Page 6 FIGURE 1 Page 6...

  • Page 7: Parts Identification

    G50UHi PARTS IDENTIFICATION (HORIZONTAL POSITION) BLOWER ASSEMBLY BLOWER HEAT EXCHANGER ACCESS PANEL ASSEMBLY BLOWER CONTROL MODULE ® SURELIGHT CONTROL BOARD BURNER ASSEMBLY COMBUSTION AIR BURNER INDUCER ACCESS PANEL PRIMARY LIMIT GAS VALVE FIGURE 2 G50UHi HEATING COMPONENTS FLUE COLLECTOR BOX...

  • Page 8: I Unit Components

    I−UNIT COMPONENTS G50UHi unit components are shown in figures 1, 2 and 3. The gas valve, combustion air inducer and burners can be accessed by removing the burner access panel. Electrical components are in the control box (figure 4) found in the blower section.
  • Page 9 TABLE 2 INTEGRATED IGNITION CONTROL 97L48 IGNITION CONTROL 97L48 J156 TERMINAL DESIGNATIONS PIN # FUNCTION Ignitor Not Used J156 Ignitor Neutral Combustion Air Inducer Line Voltage Not Used Combustion Air Inducer Neutral TABLE 3 IGNITION CONTROL 97L48 J58 TERMINAL DESIGNATIONS PIN # FUNCTION Primary Limit In...
  • Page 10 b−Fan Time Control a supply air temperature between 90° − 110° at the instant the blower is de−energized. (Longer delay times allow for The fan on time of 45 seconds is not adjustable. Fan off lower air temperature, shorter delay times allow for higher time (time that the blower operates after the heat demand air temperature).
  • Page 11 ® 5. SureLight Integrated Ignition Control INTEGRATED IGNITION CONTROL 69M15 69M15 (A92) The SureLight system consists of ignition control board (fi- gue 9), ignitor (figure 11) and sensor (figure 12). The igni- tion control and ignitor work in combination to ensure fur- nace ignition and ignitor durability.
  • Page 12 c−Electronic Ignition (See Figure 8) d−Fan Time Control Heating On a call for heat the SureLight control monitors the com- The heating fan on time of 45 seconds is not adjustable. bustion air inducer prove switch. The control will not begin Fan off time (time that the blower operates after the heat the heating cycle if the prove switch is closed (by−passed).
  • Page 13 Remove the cover panel from the module to access the se- lector jumpers. There are five selector pins in each column. G50UHi units are equipped with a blower control module These pins, when jumpered, correspond with four selec- which offers a variety of indoor blower speeds for selection.
  • Page 14 TABLE 9 Blower Mode Available Options Factory Default Cool Speeds 1, 3, 4 Speed 1 Heat (3−ton) Speeds 1, 2, 3, 4 Speed 3 Heat (4 & 5−ton) Speeds 2, 3, 4, 5 Speed 4 Speeds 2, 5, 6, 7 Speed 7 Dehumidification Speeds 3, 4, 5, 6...
  • Page 15 2 3/8" Flue Outlet Horizontal Applications FIGURE 15 The G50UHi furnace can be installed in horizontal applica- tions. The combustion air inducer may be rotated clockwise or 10. Flame Rollout Switches (S47) counterclockwise by 90° to allow for vertical vent discharge in a horizontal application.
  • Page 16 11. Primary Limit Control (S10) WHITE RODGERS 36E SERIES GAS VALVE The primary limit (S10) on G50UHi units is located in the heat- ing vestibule panel. When excess heat is sensed in the heat MANIFOLD PRESSURE exchanger, the limit will open. If the limit is open, the furnace...

  • Page 17: Installation

    IV−HEATING SYSTEM SERVICE CHECKS before starting unit. A−C.S.A. Certification B−Heating Start-Up All units are C.S.A. (formally A.G.A. and C.G.A. combined) design certified without modifications. Refer to the G50UHi Installation Instruction. WARNING B−Gas Piping Shock and burn hazard. G50UHi units are equipped CAUTION with a hot surface ignition system.
  • Page 18 Manifold pressure for the G50UHi can be mea- power to unit. These controls should be properly sured at any time the gas valve is open and is supplying gas labeled by the installer.
  • Page 19 To Measure Flame Signal − Ignition Control: transducer (Part GAS METER CLOCKING CHART TRANSDUCER #78H5401 available from Seconds for One Revolution (PART #78H5401) Lennox Repair Parts) is Natural G50UH G50UH required to measure flame Unit 1 cu ft 2 cu ft...

  • Page 20: Typical Operating Characteristics

    If the temperature is too low, decrease Filters blower speed. If temperature is too high, first check the All G50UHi filters are installed external to the unit. Filters firing rate. Provided the firing rate is acceptable, in- should be inspected monthly. Clean or replace the filters crease blower speed to reduce temperature.
  • Page 21 13− To clean the burner, run a vacuum cleaner with a soft brush attachment over the face of burners. Visually in- spect inside the burners and crossovers for any blockage G50UHi BURNER & HEAT caused by foreign matter. Remove any blockage. EXCHANGER REMOVAL 14−...

  • Page 22: Wiring And Sequence Of Operation

    VII− WIRING AND SEQUENCE OF OPERATION Page 22...
  • Page 23 G50UHi−8 5 − Gas valve opens for a 4−second trial for ignition. 1 − When there is a call for heat, W1 of the thermostat energizes 6 − Flame is sensed, gas valve remains open for the heat call. W of the furnace control with 24VAC.
  • Page 24 SURELIGHT CONTROL HEATING SEQUENCE OF OPERATION Control board 69M15 LED #1 = DS1, LED #2 = DS2 Control board 97L48 LED #1 = DIAG1 LED #2 = DIAG2 NORMAL HEATING MODE ABNORMAL HEATING MODE POWER ON GAS VALVE OFF. COMBUSTION AIR INDUCER ON. INDOOR BLOWER ON.
  • Page 25 NORMAL HEATING MODE ABNORMAL HEATING MODE 15-SECOND COMBUSTION AIR INDUCER PREPURGE INITIATED BY CLOSED PRESSURE SWITCH. IS VOLTAGE ABOVE 75 VOLTS? LEDS SIGNAL IGNITOR WARM-UP −− 20 SECONDS. ALTERNATING IS THERE A PROPER GROUND? FAST FLASH IS IGNITOR INTACT AND CONNECTED? 4-SECOND TRIAL FOR IGNITION.
  • Page 26 SURELIGHT CONTROL COOLING SEQUENCE OF OPERATION NORMAL COOLING MODE ABNORMAL COOLING MODE POWER ON IGNITION CONTROL MAIN POWER ON. GAS VALVE OFF. COMBUSTION AIR INDUCER OFF. INDOOR BLOWER OFF WITH NORMAL DELAY. CONTROL SELF DIAGNOSTIC CHECK. SIGNAL CIRCUIT BOARD FAILURE AT LED. IS CONTROL OPERATING NORMALLY? INTERRUPT MAIN POWER TO RESET CONTROL.
  • Page 27 SURELIGHT CONTROL CONTINUOUS FAN SEQUENCE OF OPERATION LED: SLOW FLASH RATE REMAINS UNCHANGED THROUGHOUT SEQUENCE. MANUAL FAN SELECTION MADE AT THERMOSTAT. CONTROL (G) ENERGIZES INDOOR BLOWER ON CONTINUOUS BLOWER SPEED. ELECTRONIC AIR CLEANER TERMINAL IS ENERGIZED. HEATING ACCESSORY TERMINAL THERMOSTAT CALLS FOR HEAT (W). ENERGIZESWITH COMB.

  • Page 28: Troubleshooting

    VIII− TROUBLESHOOTING A−SureLight Control UPON INITIAL POWER UP, REMOVE ALL THERMOSTAT DEMANDS TO THE UNIT PROBLEM: 1 UNIT FAILS TO OPERATE IN THE COOLING, HEATING, OR CONTINUOUS FAN MODE Condition Possible Cause Corrective Action / Comments 1.1.1 ACTION 1 − Check 120V main voltage. −...
  • Page 29 PROBLEM 1: UNIT FAILS TO OPERATE IN THE COOLING, HEATING, OR CONTINUOUS FAN MODE Condition Possible Cause Corrective Action / Comments ACTION 1 − Check that the unit is properly 1.5.1 ground. − On initial power−up the combustion ACTION 2 − Install a proper main ground to the Improper ground to the unit.
  • Page 30 PROBLEM 3: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR INDUCER DOES NOT ENERGIZE (CONT.). Condition Possible Cause Corrective Action/Comments 3.3.1 − Unit operates with a cooling and con- ACTION 1 − Check for correct wiring and loose tinuous fan demand.
  • Page 31 PROBLEM 5: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER ENERGIZES, IGNITOR IS ENERGIZED. Condition Possible Cause Corrective Action/Comments ACTION 1 − Check line pressure at the gas valve. 5.1.1 Pressure should not exceed 13" WC for both nat- −...
  • Page 32 PROBLEM 6: BURNERS LIGHT WITH HEATING DEMAND BUT UNIT SHUTS DOWN PREMATURELY (CONT.) Condition Possible Cause Corrective Action/Comments ACTION 1 − Check that the manifold pressure matches value listed on nameplate. See installa- − Combustion air inducer energizes 6.3.1 tion instructions for proper procedure. with a heating demand.
  • Page 33 PROBLEM 6: BURNERS LIGHT WITH HEATING DEMAND BUT UNIT SHUTS DOWN PREMATURELY (CONT.) − Combustion air inducer energizes ACTION 1 − Check that the sensor is properly lo- 6.5.1 with a heating demand. cated. ACTION 2 − Check that the sense wire is properly Loose sensor wire connection causes −...
  • Page 34 B−INDOOR BLOWER CONTROL MODULE PROBLEM Indoor blower motor does not operate with heating, cooling or continuous fan demand. CHECK WIRING D Ensure that 6−pin connector is securely plugged into blower control module. D Ensure that 3−pin motor connector is securely connected. D Check power supply wiring to blower control module from 120HOT and neutral terminals on SureLight®...
  • Page 35 CAUTION The blower control module and single−tap motor used in G50UHi units are designed specifically for use with one another. If a PSC blower motor is used to provide emergency operation, the PSC motor must be connected to the SureLight®...

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