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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
Shipping and Packing List ..............................................4
Safety Information ..........................................................4
Use of Furnace as Construction Heater .........................5
General ...........................................................................5
Combustion, Dilution & Ventilation Air ............................6
Setting Equipment ........................................................10
Filters ............................................................................ 11
Duct System / Venting ..................................................12
Gas Piping ....................................................................18
Electrical .......................................................................20
the
refrigerant
detection
INSTALLATION
INSTRUCTIONS
SL280DFVK
DAVE LENNOX SIGNATURE
DOWNFLOW AIR DISCHARGE
508559-01
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.
The Lennox iComforti
must be used in 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
which begin on Page 21.
Ignition Control .............................................................24
Integrated Control DIP Switch Settings - ......................32
Low GWP Applications .................................................37
Blower Data ..................................................................40
Unit Start-Up .................................................................42
Proper Combustion.......................................................43
High Altitude .................................................................43
Heating Sequence of Operation ...................................45
Service..........................................................................47
Repair Parts List ...........................................................48
Program Unit Capacity / Size Mode .............................51
Troubleshooting ............................................................52
Start Up and Performance Checklist ............................55
Page 1
GAS FURNACE
®
WARNING
NOTICE
communicating thermostat
®
applications,
any
both
communicating
and
Lennox
non-
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Table of Contents
Troubleshooting
Related Manuals for Lennox SL280DFVK
Summary of Contents for Lennox SL280DFVK
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Page 1: Table Of Contents
Lennox conventional thermostat may be used, as well as other This furnace is equipped with an ignition control non-communicating thermostats. factory enabled for use with Lennox A2L refrigerant In all cases, setup is critical to ensure proper system 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 SECONDARY LIMIT GASKET FLUE CHASE CONTROL BOX (Includes two-stage integrated control, transformer and circuit breaker) INTERNAL FLUE PIPE ASSEMBLY DOOR INTERLOCK SWITCH PRIMARY LIMIT LOCATION HEAT EXCHANGER COMBUSTION AIR INDUCER PRESSURE SWITCHES COMBUSTION AIR INDUCER GAS VALVE INNER BLOWER ACCESS PANEL BURNER BOX ASSEMBLY ACCESS PANEL... -
Page 4: Shipping And Packing List
80°F (27°C) must be maintained. compatible with: • Air filters must be installed in the system and must be Lennox communicating thermostats. aintained during construction. Non-communicating thermostats - ComfortSense or other • Air filters must be replaced upon construction comple- conventional thermostats. -
Page 5: Use Of Furnace As Construction Heater
SL280DFVK units may be used for heating of buildings or • When the furnace is installed in an attic or other... -
Page 6: Combustion, Dilution & Ventilation Air
In the absence of local codes concerning air for combus- Masonry acid washing materials tion and ventilation, use the guidelines and procedures in this section to install SL280DFVK furnaces to ensure effi- cient and safe operation. You must consider combustion In addition to providing combustion air, fresh outdoor air air needs and requirements for exhaust vents. -
Page 7: Confined Space
Confined Space Air from Inside A confined space is an area with a volume less than 50 If the confined space that houses the furnace adjoins a cubic feet (1.42 m3) per 1,000 Btu (.29 kW) per hour of space categorized as unconfined, air can be brought in by the combined input rating of all appliances installed in that providing two permanent openings between the two spac- space. - Page 8 EQUIPMENT IN CONFINED SPACE ALL AIR FROM OUTSIDE (Inlet Air from Crawlspace and Outlet Air to Ventilated Attic) CHIMNEY OR GAS VENT VENTILATION LOUVERS (Each end of attic) OUTLET WATER FURNACE HEATER INLET VENTILATION LOUVERS (For unheated crawl space) AIR FLOW NOTE-The inlet and outlet air openings shall each have a free area of at least one square inch (645 ) per 4,000 Btu (1.17 kW) per hour of the total input rating of all equipment in the enclosure.
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Page 9: Supply Air
CAUTION Downflow Installation Downflow unit installs in three ways: on non-combustible The furnace and downflow combustible flooring base flooring, on combustible flooring using a downflow com- shall not be installed directly on carpeting, tile, or other bustible flooring base, or on a reverse-flow cooling cabi- combustible material other than wood flooring. -
Page 10: Setting Equipment
COOLING COIL devices, which could result in personal injury or death. Install the SL280DFVK gas furnace as shipped in the down- PROPERLY PLENUM flow position only. Do not install the furnace horizontally. -
Page 11: Filters
Horizontal Front Back FIGURE 12 Downflow Application CAUTION Allow for clearances to combustible materials as indicated If this unit is being installed in a space serviced by an on the unit nameplate. Minimum clearances for closet or exhaust fan, power exhaust fan, or other device which alcove installations are shown in FIGURE 13. -
Page 12: Duct System / Venting
If the pressure drop is too great, system capacity The SL280DFVK series units are classified as fan-assist- and performance may be reduced. ed Category I furnaces when vertically vented according to the latest edition of National Fuel Gas Code (NFPA 54 The pressure drop may also cause the limit to trip / ANSI Z223.1). -
Page 13: Vent Connection
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 Connector Length feet Diameter inches suitable for venting SL280DFVK series units. The chim- ney passageway must be checked periodically to ensure 4-1/2 that it is clear and free of obstructions.
- Page 15 14 - All venting pipe passing through floors, walls, and 18 - The common vent diameter must always be at least ceilings must be installed with the listed clearance as large as the largest vent connector diameter.19 to combustible materials and be fire stopped - In no case, shall the vent connector be sized more according to local codes.
- 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...
- Page 17 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.
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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: Electrostatic Discharge (Esd)
TABLE 9. and tools to metal prior to handling the control. TABLE 9 Maximum Over-Current WARNING SL280DFVK MODEL Protection (Amps) Electric Shock Hazard. Can cause injury or 070V36A death. Unit must be properly grounded in 090V48B, 090V60C, 110V60C accordance with national and local codes. -
Page 20: Electrical
38% of cool speed. humidifier connections and may be connected to 2 - When the SL280DFVK is running in the heating 24V or 120V. Any humidifier rated up to one amp can mode, the indoor blower will run on the heating be connected to these terminals. - Page 21 Generator Use - Voltage Requirements • The furnace integrated control requires both correct polarity and proper ground. Both polarity and proper The following requirements must be kept in mind when grounding should be checked before attempting to specifying a generator for use with this equipment: operate the furnace on either permanent or tempo- •...
- Page 22 Optional Accessories for use with any Communicating System NOTE: ICOMMUNICATING THERMOSTAT SENSES HUMIDITY & CONTROLS HUM CONTACTS TO CYCLE HUMIDIFIER BASED 120V CONNECTIONS “HUM” CONTACT IS QUIRED. 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 22...
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Page 24: Ignition Control
Ignition Control FIGURE 23 TABLE 10 TABLE 12 1/4”QUICK CONNECT TERMINALS THERMOSTAT INPUT TERMINALS 120 VAC OUTPUT TO HUMIDIFIER LOW STAGE HEAT XMFR 120 VAC OUTPUT TO TRANSFORMER HIGH STAGE HEAT 120 VAC INPUT TO CONTROL CIRC 120 VAC OUTPUT TO CIRCULATING LOW STAGE COOL BLLOWER HIGH STAGE COOL24... - Page 25 TABLE 14 Field Wiring Applications With Conventional Thermostat 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.
- Page 26 TABLE 14 Field Wiring Applications With Conventional Thermostat (Continued) 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...
- Page 27 TABLE14 Field Wiring Applications With Conventional Thermostat (Continued) 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...
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Page 28: System Options
TABLE 14 Field Wiring Applications With Conventional Thermostat (Continued) 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. -
Page 29: Wiring Diagram
Wiring Diagram COMBUSTION AIR COMBUSTION AIR BLOWER MOTOR BLOWER MOTOR DOOR INTERLOCK IGNITOR CIRC FLAME SENSE WHT/PINK FLAME SENSOR WHITE BLACK 120V BLUE BLUE MV COM PINK PINK S102 HIGH HEAT PRESSURE SWITCH PURPLE S128 LOW HEAT PRESSURE SWITCH BLUE BLUE RO(OUT) GRN/YEL... -
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 Dip Switch Settings
Conventional Thermostat (non-communicating) Switch 3 Switch 4 Seconds SL280DFVK units are equipped with a two-stage, variable speed integrated control. This control manages ignition 90 (factory) timing, heating mode fan off delays and indoor blower speeds based on selections made using the control dip 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 Refer to TABLE 21 for operation sequence error codes. Select “c” from the Error Code Recall menu in applications including SL280DFVK, a thermostat which to clear all error codes. Button must be pressed a second features humidity control and a single-speed outdoor unit.
- Page 35 TABLE 21 OPERATING SEQUENCE SL280DFVK Non-Communicating Thermostat with Humidity Control Feature and Single-Speed Outdoor Unit OPERATING SEQUENCE SYSTEM DEMAND SYSTEM RESPONSE Thermostat Demand Relative Humidity Blower System Compre Step Comments ssor Condition Status (cool) NO CALL FOR DEHUMIDIFICATION Compressor and...
- Page 36 TABLE 22 OPERATING SEQUENCE SL280DFVK, 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...
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Page 37: Low Gwp Applications
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 27 and follow steps below: 1 - Route sensor wire #1 through provided grommet. - Page 38 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 39: 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 40: Blower 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 250 cfm. Lennox iHarmony Zoning System Applications - Minimum blower speed is 250 cfm. - Page 41 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 42: Unit Start-Up
GAS VALVE SHOWN IN ON POSITION The gas valve on the SL280DFVK unit will be equipped with either a gas control switch. Use only your hand to FIGURE 28 move the control switch. -
Page 43: Proper Combustion
If the unit fails to operate, check the following: NOTE - Pressure test adapter kit (10L34) is available from Lennox to facilitate manifold pressure measurement. 1 - Is the thermostat calling for heat? A manifold pressure tap located on the gas valve provides Are access panels securely in place? access to the manifold pressure. -
Page 44: Gas Conversion Kits
TABLE 28 Manifold Pressure Settings Manifold Pres- Manifold Pres- Manifold Pressure Supply Line sure in. wg. 0 sure in. wg. in. wg. 7500 - Pressure Unit Orifice Size Orifice Size - 4500 ft 4500 - 7500 ft 10,000 ft in. w.g. Input 0 - 7500 ft. -
Page 45: Heating Sequence Of Operation
The two-stage, variable speed integrated control used high fire (second stage) gas valve is energized and in SL280DFVK units has an added feature of an internal the indoor blower motor is energized for operation at Watchguard control. The feature serves as an automat- the high fire heating speed. - Page 46 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 30 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 ON-delay.
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Page 47: Service
At the beginning of each heating season, and to comply with the Lennox Limited Warranty, your system should be 1 - Check the operation of the ignition system, inspect checked as follows: and clean flame sensor. -
Page 48: Repair Parts List
NOTE - Use papers or protective covering in front of the The following repair parts are available through indepen- furnace during cleaning. dent Lennox dealers. When ordering parts, include the complete furnace model number listed on the CSA Inter- 1 - Turn off both electrical and gas power supplies to national nameplate -- Example: SL280DF070V36AK. -
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: Heating Sequence Of Operation
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 SWITCH INDOOR WATCHGUARD − AFTER HEAT FAN LIMIT SWITCH CODE CLOSED WITHIN 3... - 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...
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Page 52: Troubleshooting
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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Page 55: Start Up And Performance Checklist
Start-Up & Performance Check List UNIT SET UP (typical) Unit Model Number_______________ Serial Number___________________ SUPPLY Line Voltage upflow furnace shown Gas Supply Pressure Filter RETURN RETURN DUCT SYSTEM GAS SUPPLY SUPPLY AIR DUCT LP/Propane Gas Natural Gas Sealed Piping Connections Tight Insulated (if necessary) Leak Tested Registers Open and Unobstructed... - Page 56 UNIT OPERATION (typical) Combustion CO SUPPLY Thermostat Gas Manifold Pressure Temperatures upflow furnace shown Filter Blower Motor Amps Duct Static RETURN RETURN COOLING MODE HEATING MODE INDOOR BLOWER AMPS______ GAS MANIFOLD PRESSURE “W.C._____ TEMPERATURE DROP COMBUSTION SAMPLE CO CO PPM_______ ______ Return Duct Temperature _________ Supply Duct Temperature...
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