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© 2025 Lennox Industries Inc.
Dallas, Texas USA
WARNING
This furnace is equipped with an ignition control
factory enabled for use with Lennox A2L refrigerant
systems.
Disabling
functionality on A2L system is prohibited by safety
codes. Refer to furnace installation instructions for
non-A2L and non-Lennox refrigerant system setup.
Contents
Unit Dimensions - inches (mm) ......................................2
Parts Arrangement..........................................................3
SL280DFNVK Gas Furnace ...........................................4
Shipping and Packing List ..............................................4
Safety .............................................................................4
Use of Furnace as a Construction Heaterl .....................5
General ...........................................................................5
Combustion, Dilution, Ventilation Air...............................5
Setting Equipment ........................................................10
Filters ............................................................................ 11
Duct System .................................................................12
Venting .........................................................................12
Gas Piping ....................................................................17
the
refrigerant
detection
INSTALLATION
INSTRUCTIONS
SL280DFNVK
DAVE LENNOX SIGNATURE
GAS FURNACE DOWNFLOW
AIR DISCHARGE
508563-01
01/2025
THIS MANUAL MUST BE LEFT WITH THE
HOMEOWNER FOR FUTURE REFERENCE
This is a safety alert symbol and should never be
ignored. When you see this symbol on labels or in man-
uals, be alert to the potential for personal injury or death.
Improper installation, adjustment, alteration, service
or maintenance can cause property damage, personal
injury or loss of life. Installation and service must be
performed by a licensed professional HVAC installer (or
equivalent), service agency or the gas supplier.
A thermostat is not included and must be ordered
separately.
A communicating
communicating applications.
In
non-communicating
conventional thermostat may be used, as well as other
non-communicating thermostats.
In all cases, setup is critical to ensure proper system
operation.
Field
wiring
for
communicating applications is illustrated in diagrams,
which begin on Page 21.
Electrical .......................................................................19
Ignition Control .............................................................29
Blower Motor Performance ...........................................37
Low GWP Application ...................................................39
Unit Start-Up .................................................................42
Gas Pressure Measurement.........................................43
Proper Combustion.......................................................43
High Altitude .................................................................43
Other Unit Adjustments.................................................44
Sequence of Operation.................................................44
Service..........................................................................46
Repair Parts List ...........................................................48
Program Unit Capacity Size Mode ...............................49
Troubleshooting ............................................................50
Page 1
®
WARNING
NOTICE
thermostat
must
be
applications,
any
both
communicating
used
in
Lennox
and
non-
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Table of Contents
Related Manuals for Lennox SIGNATURE SL280DFNVK
Summary of Contents for Lennox SIGNATURE SL280DFNVK
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Page 1: Table Of Contents
This furnace is equipped with an ignition control In all cases, setup is critical to ensure proper system factory enabled for use with Lennox A2L refrigerant operation. systems. Disabling... -
Page 2: Unit Dimensions - Inches (Mm)
Unit Dimensions - inches (mm) 3-1/8 9/16 (79) (14) RETURN AIR OPENING FLUE OUTLET 19-7/16 9/16 (Top) (494) (14) 9/16 (14) TOP VIEW 27-3/4 1-1/2 (38) (705) Front Panel 9/16 19-7/16 9/16 (14) (494) (14) AIR FLOW ELECTRICAL INLET (Either Side) (838) 5-3/8 (137) Right GAS PIPING INLET... -
Page 3: Parts Arrangement
Parts Arrangement Blower assembly Blower assembly Internal flue pipe assembly Flue chase Control box Combustion air inducer Gas valve Heat exchanger assembly Access panel Air fuel intake assembly FIGURE 1 Page 3... -
Page 4: Sl280Dfnvk Gas Furnace
Certifications SL280DFNVK Gas Furnace SL280DFNVK units are CSA International certified. The SL280DFNVK gas furnace is equipped with a two- stage, variable speed integrated control. the control is In the USA, installation of gas furnaces must conform with compatible with: local building codes. In the absence of local codes, units Communicating thermostats. -
Page 5: Use Of Furnace As A Construction Heaterl
Use of Furnace as Construction Heater • Do not block the furnace combustion air openings Lennox does not recommend the use of SL280DFNVK with clothing, boxes, doors, etc. Air is needed for units as a construction heater during any phase of con- proper combustion and safe unit operation. -
Page 6: Unconfined Space
In the absence of local codes concerning air for combus- Unconfined Space tion and ventilation, use the guidelines and procedures in An unconfined space is an area such as a basement or this section to install SL280DFNVK furnaces to ensure ef- large equipment room with a volume greater than 50 cubic ficient and safe operation. - Page 7 Each opening must be at least 100 square inches (64516 When communicating with the outdoors through horizon- mm2). One opening shall be within 12 inches (305 mm) of tal ducts, each opening shall have a minimum free area of the top of the enclosure and one opening within 12 inches 1 square inch (645 mm2) per ,000 Btu (.56 kW) per total (305 mm) of the bottom.
- Page 8 Installation on Non-Combustible Flooring (FIGURE 7) EQUIPMENT IN CONFINED SPACE ALL AIR FROM OUTSIDE 1 - Cut floor opening keeping in mind clearances listed (All Air Through Ventilated Attic) CHIMNEY on unit rating plate. Also keep in mind gas supply OR GAS connections, electrical supply, flue and air intake VENT...
- Page 9 UNIT UNIT SUPPLY AIR PLENUM DOWNFLOW PROPERLY COMBUSTIBLE COOLING COIL SIZED FLOOR FLOORING BASE OPENING PROPERLY PLENUM SIZED FLOOR OPENING FIGURE 8 FIGURE 9 TABLE 2 Return Air Opening -- Downflow Units COMBUSTIBLE FLOOR OPENING SIZE Cabinet Front to Rear Side to Side The following steps should be taken when installing ple- num:...
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Page 10: Setting Equipment
Setting Equipment MODELS WITH 1/2 HP BLOWER MOTOR WARNING Do not install the furnace on its front, back or in the horizontal position. See FIGURE 13. Do not connect the return air ducts to the back of the furnace. Doing RIGID LEG remove shipping bolt and washer so will adversely affect the operation of the safety... -
Page 11: Filters
Lennox Product Specifications bulletin. maximum volume of combustion air required for all Additional information is provided in Service and gas appliances serviced by this space. -
Page 12: Duct System
The venting tables in this manual were extracted from the Duct System National Fuel Gas Code (NFPA 54 / ANSI Z223.1) and are Use industry-approved standards (such as those pub- provided as a guide for proper vent installation. Proper lished by Air Conditioning Contractors of America or Amer- application, termination, construction and location of vents ican Society of Heating, Refrigerating and Air Condition- must conform to local codes having jurisdiction. - Page 13 Common Venting Using Tile-Lined Interior Masonry Chimney and Combined Vent Connector MINIMUM LENGTH = AS SHORT AS PRACTICAL. INTERIOR TILE-LINED FOR MAXIMUM LENGTH SEE NOTE TO LEFT MASONRY CHIMNEY NOTE- Refer to provided venting tables for installations. NOTE - the chimney must be properly sized per provided venting tables or lined with listed metal lining system.
- Page 14 Never connect a Category I appliance to a chimney that is TABLE 4 servicing a solid-fuel appliance. If a fireplace chimney flue Connector Maximum Horizontal is used to vent this appliance, the fireplace opening must Connector Length feet Diameter inches be permanently sealed.
- Page 15 19 - In no case, shall the vent connector be sized more 21 - When connecting this appliance to an existing than two consecutive table size diameters over the dedicated or common venting system, you must size of the draft hood outlet or flue collar outlet. inspect the venting system’s general condition and look for signs of corrosion.
- Page 16 TABLE 6 Vent Connector Capacity Type B Double-Wall Vents with Type B Double-Wall Connectors Serving Two or More Category I Appliances Vent and Connector Diameter - D (inches) Height Lateral 3 inch 4 inch 5 inch 6 inch Appliance Input Rating in Thousands of Btu Per Hour (feet) (feet) TABLE 7...
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Page 17: Gas Piping
Removal of the Furnace from Common Vent Resize the common venting system to the minimum vent pipe size determined by using the appropriate tables in In the event that an existing furnace is removed from a Appendix G. (These are in the current standards of the venting system commonly run with separate gas applianc- National Fuel Gas Code ANSI Z223.1. -
Page 18: Leak Check
TABLE 8 Gas Pipe Capacity - ft3/hr (m3/hr) Nominal Internal Length of Pipe - feet (m) Iron Pipe Diameter Size Inches inches (3.048) (6.096) (9,144) (12,192) (15.240) (18.288) (21.336) (24.384) (27.432) (30,480) (mm) (mm) .622 (12.7) (17.799) (4.87) (3.34) (2.69) (2.29) (2.03) (1.84) -
Page 19: Electrical
The furnace must be isolated from the gas supply system IMPORTANT by closing the individual manual shut-off valve during any gas supply system at pressures greater than or equal to ½ When matching this gas furnace with zoning, psig. (3.48 kPa, 14 inches w.c.). This furnace and its com- defrost tempering stat or other 24V accessories, ponents are designed, manufactured and independent- It is recommended to replace the factory installed... - Page 20 400 CFM a ton. is designed to operate in a SINGLE-STAGE mode or TWOSTAGE mode using a conventional thermostat. For optimal performance in non-communicating applica- tions, Lennox recommends use of a ComfortSense 7500 ® high quality electronic digital thermostat or any other with adjustable settings for 1st stage / 2nd stage on / off differ- entials and adjustable stage timers.
- Page 21 Generator Use - Voltage Requirements • The furnace integrated control requires both correct po- larity and proper ground. Both polarity and proper ground- The following requirements must be kept in mind when ing should be checked before attempting to operate the specifying a generator for use with this equipment: furnace on either permanent or temporary power •...
- Page 22 Optional Accessories for use with any Communicating System NOTE: ICOMMUNICATING THERMOSTAT SENSES HUMIDITY & CONTROLS HUM CONTACTS TO CYCLE HUMIDIFIER BASED 120V CONNECTIONS QUIRED. “HUM” CONTACT IS CLOSED ANYTIME HUMIDITY DEMAND IS PRESENT TIONS. BUILT INTO ALL COMMUNICATING ENABLED OUT DOOR UNITS).
- Page 23 LENNOX COMMUNICATING OUTDOOR UNIT INDOOR UNIT (1 OR 2 STAGE) FLOAT SWITCH LENNOX COMMUNICATING OUTDOOR UNIT LENNOX COMMUNICATING FURNACE EL297VK, SL280VK, SL280VNK, SL297VK, SLP99VK cutting DS to R will not cause communication interuption or error code CUT* R-DS W914 FIGURE 23...
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Page 24: Wiring Connections
TABLE 10 DIP Switch Settings and On-Board Links DIP Switch 1 On Board Links Must Be Cut To Select Thermostat Thermostat Wiring Connections System Options Heating Stages 1 Heat / 1 Cool FURNACE OUTDOOR T'STAT TERM. STRIP UNIT NOTE - Use DIP switch 2 to set second-stage heat ON delay. - Page 25 TABLE 10 Con DIP Switch Settings and On-Board Links DIP Switch 1 On Board Links Must Be Cut To Select Thermostat Thermostat Wiring Connections System Options Heating Stages 2 Heat / 2 Cool FURNACE OUTDOOR (M30 T-stat) T'STAT TERM. STRIP UNIT CUT ON-BOARD LINK W915...
- Page 26 TABLE 10 Con DIP Switch Settings and On-Board Links DIP Switch 1 Wiring Connections Thermostat On Board Links Must Be Cut To Select Thermostat Heating System Options Stages Dual Fuel FURNACE HEAT PUMP T'STAT TERM. STRIP Single Stage Heat Pump CUT ON-BOARD LINK (M30 T-stat) W951...
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Page 27: System Options
TABLE 10 Con DIP Switch Settings and On-Board Links DIP Switch 1 Wiring Connections Thermostat On Board Links Must Be Cut To Select Thermostat Heating System Options Stages Dual Fuel FURNACE HEAT PUMP T'STAT TERM. STRIP Single Stage Heat Pump CUT ON-BOARD LINK (M30 T-stat) W951... -
Page 28: Wiring Diagram
Wiring Diagram BLACK 120VAC PURPLE YELLOW COMBUSTION AIR COMBUSTION AIR BLOWER MOTOR BLOWER MOTOR XFMR CIRC WHITE WHITE DOOR IGNITOR INTERLOCK HUMIDIFIER CIRC FLAME SENSE FLAME SENSOR WHITE BLACK 120V WHITE BLUE BLUE YELLOW MV COM ORANGE PURPLE PURPLE S128 HI/LOW HEAT PRESSURE SWITCH BLUE... -
Page 29: Ignition Control
Ignition Control TWO STAGE, VARIABLE SPEED, COMMUNICATING 107899- FIGURE 25 TABLE 13 TABLE 11 THERMOSTAT INPUT TERMINALS 1/4”QUICK CONNECT TERMINALS LOW STAGE HEAT 120 VAC OUTPUT TO HUMIDIFIER HIGH STAGE HEAT XMFR 120 VAC OUTPUT TO TRANSFORMER 120 VAC INPUT TO CONTROL LOW STAGE COOL CIRC 120 VAC OUTPUT TO CIRCULATING BLOWER... -
Page 30: Ignition Control Diagnostic Codes
Ignition Control Diagnostic Codes DIAGNOSTIC CODES / STATUS OF FURNACE CODE IDLE MODE (DECIMALBLINKS AT 1 HERTZ -- 0.5 SECONDS ON, 0.5 SECONDS OFF INDOOR BLOWER OPERATION: CONTINUOUS FAN MODE (COSTANT TORQUE ONLY) INDOOR BLOWER OPERATION: FOLLOWED BY CFM SETTING FOR INDOOR BLOWER (1 SECOND ON, 0.5 SECOND OFF) / CFM SETTING FOR MODE DISPLAYED (VARIALBE SPEED ONLY) COOLING STAGE (1 SECOND ON, 0.5 SECOND OFF) 1 OR 2 DISPLAYED / PAUSE / REPEAT CODES. - Page 31 Ignition Control Diagnostic Codes (continued) SOFT LOCKOUT FAULTS (60 MINUTES) UNABLE TO COMMUNICATE WITH CIRCULAR MOTOR E201 GAS VALVE RELAY (1ST OR 2ND STAGE) CONTACT SHORTED E205 HOT SURFACE IGNITOR (HSI) SENSED OPEN E207 SOFT LOCKOUT-FLAME FAILURE ON IGNITION, IGNITION RETRY>MAX, LAST FAILED RETRY DUE TO FLAME E270 FAILURE SOFT LOCKOUT-PRESSURE SWITCH OPEN, IGNITION RETRY>MAX, LAST FAILED RETRY DUE TO LPSW OPEN...
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Page 32: Integrated Control
TABLE 15 Integrated Control Switch Settings Conventional Thermostat (non-communicating) Blower Off Delay Switch Settings SL280DFNVK units are equipped with a two-stage, vari- Blower Off Delay Switch 3 Switch 4 able speed integrated control. This control manages igni- (Seconds) tion timing, heating mode fan off delays and indoor blower speeds based on selections made using the control dip 90 (factory) switches and jumpers. - Page 33 NOTE - The off portion of the selected ramp profile also Ramping Option D applies during heat pump operation in dual fuel applica- • Motor runs at 100% until demand is satisfied. tions. • Once demand is met, motor ramps down to stop. TABLE 18 Cooling Mode Speed Ramping 100% CFM...
- Page 34 Diagnostic LED (FIGURE 25) On-Board Links The seven-segment diagnostic LED displays operating Note: In communicating systems with a conventional out- status, target airflow, error codes and other information. door unit (non-communicating), the on-board clippable The table beginning on Page 45 lists diagnostic LED links must be set to properly configure the system.
- Page 35 W914 (R to DS) on SureLight® control With Heat Pump - Cut W914 (R to DS) & W951 (R to O) on SureLight® control Dave Lennox ComfortSense® 7500 thermostat to use for this application - Y2081 4 heat / 2 cool *Dehumidification blower speed is 70% of COOL speed for all units .
- Page 36 TABLE 22 OPERATING SEQUENCE SL280DFNVK, Non-Communicating Thermostat with Humidity Control Feature and Two-Speed Outdoor Unit OPERATING SYSTEM DEMAND SYSTEM RESPONSE SEQUENCE Thermostat Demand Relative Humidity Blower System Compre Step Comments ssor Condition Status (cool) NO CALL FOR DEHUMIDIFICATION Normal Operation Acceptable 70%* Compressor and indoor...
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Page 37: B Lo Wer Data
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position. Continuous Fan Only speed is selectable at 28% and 38% of the selected second stage cooling speed - minimum 380 cfm. Lennox iHarmony Zoning System Applications - Minimum blower speed is 380 cfm. - Page 38 First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position. Continuous Fan Only speed is selectable at 28% and 38% of the selected second stage cooling speed - minimum 450 cfm. Lennox iHarmony Zoning System Applications - Minimum blower speed is 450 cfm.
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Page 39: Low Gwp Application
Low GWP Application WARNING For use with Lennox approved evaporator coil and LGWP sensors only. Use original manufacturer recommended LGWP sensors if using non Lennox approved evaporator coil. CONNECTING THE FURNACE CONTROL BOARD SENSOR. See FIGURE 28 and follow steps below: 1 - Route sensor wire #1 through provided grommet. - Page 40 FURNACE CONTROL BOARD LOW GWP MODES OF NOTE - The HVAC system may not maintain a cooling or heating setpoint if a significant leak exists. Any refrigerant OPERATION leaks that remain unaddressed for an extended time may The modes of operation for the furnace control board are cause the HVAC system to shut down on a low refrigerant Initializing, Normal, Leak Detected, and Fault.
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Page 41: Start-Up Procedure
LGWP TEST BUTTON FUNCTIONALITY External Alarm (For applications with external alarms wired directly to the The furnace control board is equipped with a Test/Reset furnace control board) push button. The Test button can be used to perform sev- The furnace control board triggers the external alarm sys- eral functions, depending on the mode of operation of the tem when it enters Leak Detected mode. -
Page 42: Unit Start-Up
4 - This furnace is equipped with an ignition device Unit Start-Up which automatically lights the burners. Do not try to light the burners by hand. WARNING 5 - Remove the access panel. Do not use this furnace if any part has been 6 - Move switch on gas valve to OFF. -
Page 43: Gas Pressure Measurement
5 - Is the filter dirty or plugged? Dirty or plugged filters 2- Start unit and allow 5 minutes for unit to reach steady state. will cause the limit control to shut the unit off. 3 - After allowing unit to stabilize for 5 minutes, record 6 - Is gas turned on at the meter? manifold pressure and compare to value given in 7 - Is the manual main shut-off valve open? -
Page 44: Other Unit Adjustments
The integrated control runs a self-diagnostic program Other Unit Adjustments and checks high temperature limit switches for normally Primary Limit closed contacts and pressure switches for normally open contacts. The combustion air inducer is energized at low The primary limit is located on the heating compartment speed. - Page 45 Applications Using A Single-Stage Thermostat 4 - After the 20-second warm-up period has ended, the gas valve is energized on low fire (first stage) and See FIGURE 31 for ignition control sequence ignition occurs. At the same time, the control module B - Heating Sequence -- Control Thermostat Selection sends a signal to begin an indoor blower 30-second DIP Switch 1 ON in “Single-Stage”...
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Page 46: Service
14- Verify operation of CO detectors and replace At the beginning of each heating season, and to comply batteries as required. with the Lennox Limited Warranty, your system should 15 - Inspect the Low GWP sensor(s) and rubber sleeve. be checked as follows: Perform a general system test. -
Page 47: Cleaning The Burners
Cleaning the Burners The air intake assembly and air fuel plenum can be removed as one component NOTE - Use papers or protective covering in front of the 4- To clean burner, run a vacuum cleaner with a soft furnace during cleaning. brush attachment over the face of burner. -
Page 48: Repair Parts List
Repair Parts List The following repair parts are available through independent Lennox dealers. When ordering parts, include the complete furnace model number listed on the CSA International nameplate -- Example: SL280DF060NV36BK-01. All service must be performed by a licensed professional installer (or equivalent), service agency, or gas supplier. -
Page 49: Program Unit Capacity Size Mode
Program Unit Capacity/Size Mode Power-Up - Number displayed represents by integrated control unit size code (furnace model − − and capacity). If three horizontal bars are displayed followed by continuous E203, furnace − control does not recognize unit size code. Configure per the following: Furnace control in IDLE mode No heating, cooling or indoor fan operation) -
Page 50: Troubleshooting
Troubleshooting: Heating Sequence of Operation CALL FOR FIRST-STAGE HEAT CALL FOR 1ST STAGE HEAT (LOW FIRE) INDOOR BLOWER OFF AFTER HEAT FAN OFF DELAY (LOW HEAT SPEED) INDOOR LIMIT BLOWER OFF HIGH ERROR INDOOR SWITCH WATCHGUARD − AFTER HEAT FAN LIMIT SWITCH CODE BLOWER... - Page 51 Troubleshooting: Heating Sequence of Operation (Continued) CALL FOR SECOND-STAGE HEAT CALL FOR 2ND STAGE HEAT (HIGH FIRE) SINGLE STAGE 2 STAGE THERMOSTAT THERMOSTAT 2ND STAGE RECOGNITION DELAY ON DELAY (30 SECONDS) EXPIRED? EXPIRED? ONLY FOR 1ST REQUEST FOR 2ND STAGE HEAT INDUCER SWITCHED TO HIGH SPEED HIGH...
- Page 52 Troubleshooting: Heating Sequence of Operation (Continued) CALL FOR HEAT SATISFIED FIRST-STAGE HEAT SECOND-STAGE HEAT RUN MODE: 1ST OR 2ND STAGE CALL FOR HEAT. ALL INPUTS MONITORED (LIMIT, PRESSURE, CALL FOR HEAT/COOL, FLAME LEVEL) 2ND STAGE HEAT 2ND STAGE CALL FOR HEAT SATISFIED? DE−ENERGIZE 2ND STAGE GAS VALVE...
- Page 53 Troubleshooting: Cooling Sequence of Operation CALL FOR COOLING 1ST STAGE COOLING REQUEST RECEIVED WAIT FOR COMPRESSOR TIMED OFF DELAY TO EXPIRE ENERGIZE 1ST STAGE COOLING CONTACTOR (COMPRESSOR & FAN) INDOOR BLOWER 2 SECOND ON DELAY ENERGIZE INDOOR BLOWER (LOW COOLING MODE) MAINTAIN INDOOR BLOWER (LOW COOLING MODE)
- Page 54 Troubleshooting: Continuous Fan Sequence of Operation CALL FOR FAN CALL FOR FAN INDOOR BLOWER ON CONTINUOUS FAN SPEED CALL FOR FAN MAINTAIN INDOOR BLOWER AT REMOVED? CONTINUOUS FAN REQUEST MAINTAIN INDOOR FOR COOLING GO TO CALL FOR COOLING BLOWER AT RECEIVED? CONTINUOUS FAN REQUEST...
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