Lennox 80MGF Series Manual
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Lennox 80MGF Series Manual

Lennox 80MGF Series Manual

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Service Literature
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
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.
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80MGF SERIES UNITS
) Standards and California
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80MGF
Corp. 9801−L2
Revised 08−2004
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© 1998 Lennox Industries Inc.

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Summary of Contents for Lennox 80MGF Series

  • Page 1: Table Of Contents

    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 ) Standards and California Seasonal Efficiency requirements.

  • Page 2: Specifications

    SPECIFICATIONS Model No. 80MGF2(X)-45 80MGF2-60 80MGF3(X)-60 80MGF2-75 80MGF3(X)-75 Input Btuh (kW) 45,000 (13.2) 60,000 (17.6) 75,000 (22.0) Output Btuh (kW) 36,900 (10.8) 49,200 (14.4) 61,700 (18.1) lA.F.U.E. 80.1% 80.5% 80.1% 80.0% California Seasonal Efficiency 75.4% 76.4% 75.9% 76.8% 76.8% Flue size connection diameter in.
  • Page 3 SPECIFICATIONS continued Model No. 80MGF4(X)-75 80MGF3/4(X)-100 80MGF4/5(X)-100 Input Btuh (kW) 75,000 (22.0) 100,000 (29.3) Output Btuh (kW) 61,700 (18.1) 82,000 (24.0) lA.F.U.E. 80.0% 80.1% 80.0% California Seasonal Efficiency 76.3% 76.5% 77.0% Flue size connection diameter in. (mm) round 4 (102) _F (_C) Temperature rise range 45 - 75 (25 - 42)
  • Page 4 SPECIFICATIONS continued Model No. 80MGF4/5-140 80MGF3/4-120 80MGF4/5(X)-120 Input Btuh (kW) 140,000 (41.0) 120,000 (35.2) Output Btuh (kW) 114,800 (33.6) 98,400 (28.8) lA.F.U.E. 80.0% 80.0% 80.1% California Seasonal Efficiency Not Available Not Available 75.5% Flue size connection diameter in. (mm) round 5 (127) 4 (102) _F (_C)

  • Page 5: Blower Data

    BLOWER PERFORMANCE DATA 80MGF2-45, 80MGF2-60 AND 80MGF2-75 BLOWER PERFORMANCE Air Volume at Various Blower Speeds External Static External Static Pressure High Medium-High Medium-Low in. w.g. 1270 1245 1220 1195 1170 1140 1110 1060 NOTE All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table 80MGF3-60 AND 80MGF3-75 BLOWER PERFORMANCE Air Volume at Various Blower Speeds External Static...
  • Page 6 80MGF4-75, 80MGF3/4-100 AND 80MGF3/4-120 BLOWER PERFORMANCE Air Volume at Various Blower Speeds External Static External Static Pressure High Medium-High Medium Medium-Low in. w.g. 1830 1600 1325 1070 1815 1585 1320 1070 1800 1570 1315 1070 1875 1550 1310 1065 1750 1530 1300 1060...

  • Page 7: Parts Identification

    80MGF PARTS IDENTIFICATION and ORIENTATION VENT ADAPTER CABINET TOP HEAT EXCHANGER ASSEMBLY FLUE BOX COMBUSTION AIR PRESSURE BLOWER SWITCH 80MGF PRIMARY CABINET LIMIT FRONT ACCESS PANEL BURNER TURBULATOR ASSEMBLY TRANSFORMER CONTROL BOARD SECONDARY LIMITS CABINET BOTTOM BLOWER ASSEMBLY DOOR INTERLOCK SWITCH FIGURE 1 HEATING COMPONENTS (shown in horizontal position) PRIMARY LIMIT...
  • Page 8 80MGF BURNER ASSEMBLY (Shown With SureLight ignitor) SURELIGHT ROLLOUT IGNITOR SWITCHES BURNER BOX VEST PANEL UPPER BURNER MOUNTING RAIL LOWER BURNER MOUNTING RAIL FLAME BURNER SENSOR HEAT EXCHANGER PRIMARY LIMIT Back ORIFICE Left GAS VALVE Right Front BURNER BOX MANIFOLD Bottom FIGURE 3 80MGF BLOWER DOOR COMPONENTS −...

  • Page 9: I Unit Components

    ditions. The diagnostic LED lights red (not flashing) to indi- I−UNIT COMPONENTS (Figures 1, 2, 3) cate control board failure. Table 3 shows how to interpret the 80MGF unit components are shown in figure 1. The blower other LED modes. controls, gas valve and burners can be accessed by re- Pre-Purge moving the front access panel.
  • Page 10 RAM CONTROL (A3) SPARK OUTPUT 24VAC VOLT TERMINAL LINE VOLTAGE CONNECTIONS TERMINAL CONNECTIONS See Table 2 for Terminal Func- See Table 2 for tions Terminal Func- tions FAN-OFF TIMING SWITCHES THERMOSTAT CONNECTIONS DIAGNOSTIC FIGURE 5 TABLE 1 When flame is sensed, the indoor blower starts after a 45 second delay.
  • Page 11 Fan OFF" timings (time that the blower operates after a FAN-OFF TIME ADJUSTMENT SWITCHES heating or cooling demand has been satisfied) are de- LOCATED ON FURNACE CONTROL (A3) Fan-Off Timings termined by the arrangement of switches on the furnace Switch control board.
  • Page 12 when no voltage should be present, the control de-energizes 4− EGC Control (A3) the combustion air blower which terminates voltage to the Some early model 80MGF units are equipped with an inte- valve. The system goes into hard lock-out which is reset only grated ignition/blower control (EGC−1 or EGC−2) which con- by removing power to the unit.
  • Page 13 Troubleshooting TABLE 4 EGC DIAGNOSTIC CODES The EGC control board is equipped with two diagnostic green DIAG #2 DIAG #1 DIagnostic Condition LEDs to indicate the mode of failure. The LED lights are Power ON". Normal Operation. In- marked DIAG #1 and DIAG #2. The codes are given in table Simultaneous Simultaneous creased flash rate indicates there...
  • Page 14 6− SureLight Ignition System A3 Pressure Switch Return (−11 models) Hi Limit Return / Pressure Switch Out All 80MGF−11 model units are equipped with the Lennox Flame Sensor SureLight ignition system. The system consists of ignition Gas Valve Out control board (figure 11 with control terminal designa- High Limit Out tions in table 10) and ignitor (figure 12).
  • Page 15 TABLE 7 a−Electronic Ignition On a call for heat the SureLight control monitors the com- SureLight BOARD J156 (J2) TERMINAL bustion air blower pressure switch. The control will not be- DESIGNATIONS gin the heating cycle if the pressure switch is closed (by− PIN # FUNCTION passed).
  • Page 16 The SureLight board is equipped with two LED lights for troubleshooting. The lights are found just above the 24VAC termi- nal strip see figure 8. The diagnostic codes are listed below in table 9. TABLE 9 DIAGNOSTIC CODES MAKE SURE TO ID LED’S CORRECTLY: REFER TO INSTALLATION INSTRUCTIONS FOR CONTROL BOARD LAYOUT. LED #1 LED #2 DESCRIPTION...
  • Page 17 To Remove Blower From Unit: Remove Bolts and Wiring Jackplugs. Then Slide Out Front of Unit. LIMIT CONTROL FOR FIGURE 13 80MGF SERIES UNITS THIS TYPE AUTO-RESET LIMIT C−Combustion Air Blower (B6) IS USED FOR THE PRIMARY LIMIT (S10) AND...
  • Page 18 Refer to figures FIGURE 16 19 or 20 for location of valve features. An LPG changeover kit is available from Lennox. The kit in- cludes burner orifices and a regulator conversion kit. TYPICAL BURNER/ELECTRODE ORIENTATION 23/32 in.

  • Page 19: Installation

    If the knob will not turn by hand, do not try to repair it, (Pressure) Switch (S64) call a qualified service technician. Force or attempted repair 80MGF series units are equipped with a combustion air may result in a fire or explosion. prove switch located on the vestibule panel. The switch is connected to the combustion air blower housing by means of a flexible silicone hose.

  • Page 20: Preliminary Seasonal Checks

    A−Preliminary and Seasonal Checks C−Safety or Emergency Shutdown 1− Inspect electrical wiring, both field and factory installed Turn off unit power. Close manual and main gas valves. for loose connections. Tighten as required. D−Extended Period Shutdown 2− Check voltage at disconnect switch. Voltage must be within range listed on the nameplate.
  • Page 21 Gas Leak Detector is strongly recommended. It is available 1− Connect a test gauge to outlet pressure tap on gas through Lennox under part number 31B2001. See Corp. valve. Start unit and allow 5 minutes for unit to reach 8411−L10, for further details.

  • Page 22: Typical Operating Characteristics

    the ignition control sensor connection and the nega- G−High Altitude Derate tive (−) lead of the meter to the sensor wire. See figure NOTE−In Canada, certification for installation at alti- tudes over 4500 ft. (1372m) above sea level is the juris- 2−...
  • Page 23 TABLE 17 To Measure Temperature Rise: BLOWER SPEED SELECTION 1 − Place plenum thermometers in the supply and return Factory Connected air plenums. Locate supply air thermometer in the first Speeds Speed Taps Unit Unit horizontal run of the plenum where it will not pick up ra- Available Available Cool (Black)

  • Page 24: Maintenance

    Make adjustments, if necessary. death. See adjustments section. B−Supply Air Blower 1 − Check and clean blower wheel. 2 − Motors used on the Lennox 80MGF series units are permanently lubricated and need no further lu- brication. Page 24...
  • Page 25 C−Flue and Chimney CAUTION Flue must conform to all AGA/GAMA venting require- ments. Flue pipe deteriorates from the inside out and must Potential for gas leaks, fire or explosion. be disconnected in order to check thoroughly. Check flue Some soaps used for leak detection are corrosive to certain metals.

  • Page 26: Wiring And Sequence Of Operation

    VII−WIRING AND SEQUENCE OF OPERATION 80MGF WITH RAM CONTROL 5- When S18 closes, assuming the flame rollout switch (S47) primary limit (S10) and secondary limits (S21) 1- When disconnect is closed, 120V is routed through are closed, the furnace control begins a 45 second door interlock switch (S51) to feed the line voltage time-delay (pre-purge).
  • Page 27 80MGF TROUBLESHOOTING SEQUENCE NORMAL HEATING MODE ABNORMAL HEATING MODE LED: SLOW FLASH RATE THERMOSTAT CALLS FOR HEAT LED: FAST FLASH RATE LOCKOUT: MAIN VALVE OFF COMB. AIR AND SYSTEM FANS ON RESET THERMOSTAT FLAME OFF? LED: 5 flash if flame sensed with valve off LED: Steady on if control board failure CONTROL SELF−CHECK OKAY? CHECK TO SEE IF MAIN VALVE IS OFF.
  • Page 28 80MGF TROUBLESHOOTING SEQUENCE − COOLING LED: Slow flash rate. REMAINS UNCHANGED THROUGHOUT COOLING CYCLE. THERMOSTAT CALLS FOR COOLING. COMPRESSOR CONTACTOR AND SYSTEM FAN ENERGIZED AT COOLING SPEED AFTER 1 SECOND DELAY. THERMOSTAT OPENS. COMPRESSOR OFF. SYSTEM FAN OFF AFTER COMPLETING SELECTED DELAY INTERVAL (At dip switches).
  • Page 29 80MGF WITH EGC−2 IGNITION CONTROL 1 − When disconnect is closed, 120V is routed through door 5 − When S18 closes, assuming primary limit (S10) and interlock switch (S51) to feed the line voltage side of the secondary limit (S21) are closed, a 15 second pre−purge ignition control (A3) and transformer T1 primary.
  • Page 30 80MGF WITH EGC−2 HEATING SEQUENCE OF OPERATION ABNORMAL HEATING MODE NORMAL HEATING MODE GAS VALVE OFF. COMB. BLOWER ON. INDOOR CONTROL MAIN POWER ON" BLOWER ON HEAT SPEED. SEQUENCE HOLDS UNTIL NO FLAME SENSED OR MAIN POWER IS INTERRUPTED FLAME OFF? AND RESET.
  • Page 31 80MGF WITH EGC−2 COOLING SEQUENCE OF OPERATION LED: Slow flash rate. REMAINS UNCHANGED THROUGHOUT COOLING CYCLE. THERMOSTAT CALLS FOR COOLING. COMPRESSOR CONTACTOR AND SYSTEM FAN ENERGIZED AT COOLING SPEED AFTER 1 SECOND DELAY. ACC TERMINAL ENERGIZED. THERMOSTAT OPENS. COMPRESSOR OFF. SYSTEM FAN AND ACC TERMINAL OFF AFTER 0 SECONDS.
  • Page 32 80MGF WITH EGC−1 IGNITION CONTROL 1 − When disconnect is closed, 120V is routed through door 5 − When S18 closes, assuming primary limit (S10) and interlock switch (S51) to feed the line voltage side of the secondary limit (S21) are closed, a 15 second pre−purge ignition control (A3) and transformer T1 primary.
  • Page 33 80MGF WITH EGC−1 HEATING SEQUENCE OF OPERATION ABNORMAL HEATING MODE NORMAL HEATING MODE GAS VALVE OFF. COMB. BLOWER ON. INDOOR CONTROL MAIN POWER ON" BLOWER ON HEAT SPEED. SEQUENCE HOLDS UNTIL NO FLAME SENSED OR MAIN POWER IS INTERRUPTED FLAME OFF? AND RESET.
  • Page 34 80MGF WITH EGC−1 COOLING SEQUENCE OF OPERATION LED: Slow flash rate. REMAINS UNCHANGED THROUGHOUT COOLING CYCLE. THERMOSTAT CALLS FOR COOLING. COMPRESSOR CONTACTOR AND SYSTEM FAN ENERGIZED AT COOLING SPEED AFTER 1 SECOND DELAY. ACC TERMINAL ENERGIZED. THERMOSTAT OPENS. COMPRESSOR OFF. SYSTEM FAN AND ACC TERMINAL OFF AFTER 0 SECONDS.
  • Page 35 80MGF WITH SURELIGHT IGNITION CONTROL 1 − When there is a call for heat, W1 of the thermostat en- 5 − Gas valve opens for a 4−second trial for ignition. ergizes W of the furnace control with 24VAC. 6 − Flame is sensed, gas valve remains open for the heat 2 −...
  • Page 36 SURELIGHT CONTROL HEATING SEQUENCE OF OPERATION NORMAL HEATING MODE ABNORMAL HEATING MODE POWER ON GAS VALVE OFF. COMBUSTION AIR BLOWER ON. INDOOR BLOWER ON. LED #1 ALTERNATING FAST FLASH CONTROL SELF−CHECK OKAY? LED#2 ALTERNATING FAST FLASH CHECK FOR BROKEN IGNITOR OR OPEN IGNITOR CIRCUIT COMBUSTION AIR BLOWER ON FOR 1 SECOND.
  • Page 37 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 38 SURELIGHT CONTROL COOLING SEQUENCE OF OPERATION NORMAL COOLING MODE ABNORMAL COOLING MODE POWER ON IGNITION CONTROL MAIN POWER ON. GAS VALVE OFF. COMBUSTION AIR BLOWER 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 39 SURELIGHT CONTROL CONTINUOUS LOW SPEED FAN SEQUENCE OF OPERATION LED: SLOW FLASH RATE REMAINS UNCHANGED THROUGHOUT SEQUENCE. MANUAL FAN SELECTION MADE AT THERMOSTAT. CONTROL (G) ENERGIZES SYSTEM FAN AT ACB LOW SPEED. ACC. TERMINAL IS ENERGIZED. HTG ACC. TERM. ENERGIZES THERMOSTAT CALLS FOR HEAT (W).

  • Page 40: Surelight Control Troubleshooting

    VIII−Troubleshooting−SureLight Control 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. − Both diagnostic lights fail to light up. Main voltage 120V not supplied to Determine cause of main power failure.
  • Page 41 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 grounded. − On initial power−up the combustion ACTION 2 − Install a proper main ground to the Improper ground to the unit.
  • Page 42 PROBLEM 3: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER DOES NOT ENERGIZE (CONT.). Condition Possible Cause Corrective Action/Comments − Unit operates with a cooling and con- 3.3.1 ACTION 1 − Check for correct wiring and loose tinuous fan demand.
  • Page 43 PROBLEM 5: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER ENERGIZES, IGNITOR IS ENERGIZED. (CONT.) Condition Possible Cause Corrective Action/Comments ACTION 1 − Check line pressure at the gas 5.1.1 valve. Pressure should not exceed 13" WC for −...
  • Page 44 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 blower energizes tion instructions for proper procedure. with a heating demand.
  • Page 45 PROBLEM 6: BURNERS LIGHT WITH HEATING DEMAND BUT UNIT SHUTS DOWN PREMATURELY (CONT.) − Combustion air blower energizes with a heating demand. − Burners light. − Diagnostic lights flash watch guard 6.5.1 ACTION 1 − Check that the sensor is properly lo- flame failure.
  • Page 46 SERVICE NOTES Page 46...

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