Lennox SLP99DF070XV36B Installation and operation manual

Page 1 ©2021 Lennox Industries Inc.
100002
05/2021
SLP99DFV
Service Literature
SLP99DFV SERIES UNITS
SLP99DFV series units are high-efficiency downflow gas
furnaces equipped with variable capacity gas valve, vari
able speed combustion air inducer and variable speed in
door blower motor. All models are designed for direct vent
(dual pipe) venting system only. SLP99DFV units are avail
able in heating capacities from 66,000 to 132,000 Btuh
(19.3 to 38.6 kW) and cooling applications from 2 to 5 tons
(7.0 kW to 17.5 kW). Refer to Engineering Handbook for
proper sizing.
Units are factory-equipped for use with natural gas. Kits are
available for conversion to LP operation. SLP99DFV models
include a SureLight®variable integrated control that can be
used with a communication thermostat as part of a commu
nicating comfort system. All SLP99DFV units meet the Cali
fornia Nitrogen Oxides (NOx) Standards and California Sea
sonal Efficiency requirements.
All specifications in this manual are subject to change. Pro
cedures outlined in this manual are presented as recom
mendations 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 recommendations only and do not consti
tute code.
TABLE OF CONTENTS
Specifications Page 2.............................
Optional Accessories Page 3......................
Blower Data Page 4..............................
I Unit Components Page 10.......................
II Communicating Thermostat Page 36..............
III Placement and Installation Page 39..............
IV Start Up Page 55..............................
V Heating System Service Checks Page 56..........
VI Typical Operating Characteristics Page 61........
VII Maintenance Page 61..........................
VIII Wiring and Sequence of Operation Page 64.....
IX Field Wiring Page 72...........................
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
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.
CAUTION
As with any mechanical equipment, contact with
sharp sheet metal edges can result in personal injury.
Take care while handling this equipment and wear
gloves and protective clothing.

Page 2
SPECIFICATIONS
Gas
Heating
Performance
Model No. SLP99DF070XV36B SLP99DF090XV36C SLP99DF090XV48C
1AFUE 97.5% 97.5% 97.5%
Maximum Input - Btuh 66,000 88,000 88,000
Output - Btuh 64,000 84,000 85,000
Temperature rise range - °F 50 - 80 60 - 90 50 - 80
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
3.5 / 10.0 3.5 / 10.0 3.5 / 10.0
Minimum Input - Btuh 23,000 31,000 31,000
Output - Btuh 22,000 30,000 30,000
Temperature rise range - °F 35 - 65 35 - 65 35 - 65
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
0.5 / 1.5 0.5 / 1.5 0.5 / 1.5
High static - in. w.g. 0.8 0.8 0.8
Connections
in.
Intake / ² Exhaust Pipe (PVC) 2 / 2 2 / 2 2 / 2
Gas pipe size IPS 1/2 1/2 1/2
Condensate Drain Trap (PVC pipe) - i.d. 3/4 3/4 3/4
with furnished 90° street elbow 3/4 slip x 3/4 Mipt 3/4 slip x 3/4 Mipt 3/4 slip x 3/4 Mipt
with eld supplied (PVC coupling) - o.d. 3/4 slip x 3/4 MPT 3/4 slip x 3/4 MPT 3/4 slip x 3/4 MPT
Indoor
Blower
Wheel nominal diameter x width - in. 10 x 9 10 x 9 11 x 11
Motor output - hp 1/2 1/2 3/4
Tons of add-on cooling 2 - 3 2 - 3 3 - 4
Air Volume Range - cfm 410 - 1365 465 - 1385 545 - 1745
Electrical Data Voltage (Maximum Amps) 120 volts - 60 hertz - 1 phase
Blower motor full load amps 7.7 7.7 10.1
Maximum overcurrent protection 15 15 15
Shipping Data lbs. - 1 package 141 156 166
NOTE - Filters and provisions for mounting are not furnished and must be eld provided.
1 Annual Fuel Utilization E󰀩ciency based on DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized furnaces.
22 in. Rubber Flue Coupling is furnished for exhaust pipe connection to unit.
SPECIFICATIONS
Gas
Heating
Performance
Model No. SLP99DF090XV60C SLP99DF110XV60C
1AFUE 97.5% 97.5%
Maximum Input - Btuh 88,000 110,000
Output - Btuh 85,000 107,000
Temperature rise range - °F 50 - 80 50 - 80
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
3.5 / 10.0 3.5 / 10.0
Minimum Input - Btuh 31,000 39,000
Output - Btuh 30,000 38,000
Temperature rise range - °F 35 - 65 35 - 65
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
0.5 / 1.5 0.5 / 1.5
High static - in. w.g. 0.8 0.8
Connections
in.
Intake / ² Exhaust Pipe (PVC) 2 / 2 2 / 2
Gas pipe size IPS 1/2 1/2
Condensate Drain Trap (PVC pipe) - i.d. 3/4 3/4
with furnished 90° street elbow 3/4 slip x 3/4 Mipt 3/4 slip x 3/4 Mipt
with eld supplied (PVC coupling) - o.d. 3/4 slip x 3/4 MPT 3/4 slip x 3/4 MPT
Indoor
Blower
Wheel nominal diameter x width - in. 11 x 11 11 x 11
Motor output - hp 1 1
Tons of add-on cooling 3.5 - 5 3.5 - 5
Air Volume Range - cfm 467 - 2130 575 - 2180
Electrical Data Voltage (Maximum Amps) 120 volts - 60 hertz - 1 phase
Blower motor full load amps 12.8 12.8
Maximum overcurrent protection 20 20
Shipping Data lbs. - 1 package 166 175
NOTE - Filters and provisions for mounting are not furnished and must be eld provided.
1 Annual Fuel Utilization E󰀩ciency based on DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized furnaces.
22 in. Rubber Flue Coupling is furnished for exhaust pipe connection to unit.

Page 3
OPTIONAL ACCESSORIES - ORDER SEPARATELY
NOTE - FURNACES CANNOT BE TWINNED!
“B” Width Models “C” Width Models
CABINET ACCESSORIES
Downow Combustible Flooring Base 11M60 11M61
High Performance Economizer (Commercial Only) 10U53 10U53
CONDENSATE DRAIN KITS
Condensate Drain Heat Cable 6 ft. 26K68 26K68
24 ft. 26K69 26K69
Crawl Space Vent Drain Kit US 51W18 51W18
Canada 15Z70 15Z70
CONTROLS
iComfort®S30 Ultra-Smart Wi-Fi Thermostat 12U67 12U67
1Remote Outdoor Temperature Sensor X2658 X2658
2Discharge Air Temperature Sensor 88K38 88K38
Night Service Kit 15X37 15X37
DOWNFLOW FILTER KITS
Downow Air Filter and Rack Kit 51W07 51W08
No. and Size of lter - in. (2) 16 x 20 x 1 (2) 16 x 20 x 1
TERMINATION KITS
Direct Vent Applications Only. See Installation Instructions for specic venting information.
Termination Kits Concentric US - 2 in. 71M80 69M29
3 in. - - - 60L46
Canada - 2 in. 44W92 44W92
3 in. - - - 44W93
Flush-Mount US - 2, 2-1/2 or 3 in. 51W11 51W11
Canada - 2, 2-1/2 or 3 in. 51W12 51W12
Wall - Close
Couple
US - 2 in. 22G44 - - -
3 in. 44J40 44J40
Wall - Close
Couple WTK
Canada - 2 in. 30G28 - - -
3 in. 81J20 81J20
Roof 2 in. 15F75 15F75
Wall Ring Kit 2 in. 15F74 15F74
Roof Termination Flashing Kit (2 ashings) 3 in. 44J41 44J41
VENTING
3Left Side Vent Kit 2 or 3 in. 87W73 87W73
1Remote Outdoor Temperature Sensor is used with conventional (non-iComfort®Communicating) outdoor units (sensor is furnished with iComfort®Communicating
outdoor units). Allows the thermostat to display outdoor temperature. Required in dual-fuel and EDA applications.
2Optional for service diagnostics.
3NOTE - The curved exhaust pipe furnished with the Left Side Vent Kit counts as one additional 2 in. diameter 90° elbow. When using 3 in. diameter pipe, the furnished
curved exhaust pipe and eld provided ttings to transition from 2 in. to 3 in. count as 20 feet of equivalent pipe on all units.
NOTE - Termination Kits (44W92, 44W93, 30G28, 51W12, 81J20) and Crawl Space Vent Drain Kit (15Z70) are certied to ULC S636 standard for use in Canada only.

Page 4
BLOWER DATA
SLP99DF070XV36B BLOWER PERFORMANCE (less lter)
HEATING BLOWER PERFORMANCE - 0 through 0.8 in. w.g. External Static Pressure Range
Heating Adjust CFM Selections Heating Input Range and Blower Volume - CFM
35% 40% 50% 60% 70% 80% 90% 100%
Increase (+15%) Heat CFM 495 543 639 735 830 926 1022 1118
Increase (+7.5%) Heat CFM 473 516 604 691 778 866 953 1041
Default Heat CFM 450 489 568 647 726 805 884 963
Decrease (-7.5% ) Heat CFM 430 467 540 614 687 761 834 908
Decrease (-15% ) Heat CFM 410 444 512 580 649 717 785 853
COOLING BLOWER PERFORMANCE - 0 through 1.0 in. w.g. External Static Pressure Range
Cooling Adjust CFM
Selections
Blower Speed Selections
First Stage Cool Speed - cfm Second Stage Cool Speed - cfm
Low Medium-
Low
Medium
High
High
(Default)
Low Medium-
Low
Medium
High
High
(Default)
Increase (+10%) Cool CFM 625 785 890 995 910 1075 1230 1365
Default Cool CFM 575 710 830 890 845 960 1125 1265
Decrease (-10%) Cool CFM 520 615 710 820 755 885 985 1150
The e󰀨ect of static pressure is included in air volumes shown.
The following control congurations are available. See Installation Instructions for details and DIP switch settings.
Heat Modes Available (Heating Blower Performance Table):
Single-stage thermostat:
- 35%, 70%, 100% input (three-stage) with time delays in-between
Two-stage thermostat:
- Variable Rate Capacity Mode - furnace automatically adjusts ring rate based on rst- and second-stage cycle times.
- W1 demand at 70% input, W2 demand at 100% input. No delay between stages.
Cool Mode Available (Cooling Blower Performance Table):
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan speeds are approximately 28% and 38% (DIP switch selectable) of the same second-stage COOL speed position minimum 250 cfm.
Lennox iHarmony® Zoning System Applications - Minimum blower speed is 250 cfm.

Page 5
BLOWER DATA
SLP99DF090XV36C BLOWER PERFORMANCE (less lter)
HEATING BLOWER PERFORMANCE - 0 through 0.8 in. w.g. External Static Pressure Range
Heating Adjust CFM Selections Heating Input Range and Blower Volume - CFM
35% 40% 50% 60% 70% 80% 90% 100%
Increase (+15%) Heat CFM 710 756 848 940 1033 1125 1217 1309
Increase (+7.5%) Heat CFM 670 713 799 885 971 1057 1143 1230
Default Heat CFM 629 669 749 829 910 990 1070 1150
Decrease (-7.5% ) Heat CFM 559 599 681 763 845 927 1009 1091
Decrease (-15% ) Heat CFM 488 530 614 697 781 865 948 1032
COOLING BLOWER PERFORMANCE - 0 through 1.0 in. w.g. External Static Pressure Range
Cooling Adjust CFM
Selections
Blower Speed Selections
First Stage Cool Speed - cfm Second Stage Cool Speed - cfm
Low Medium-
Low
Medium
High
High
(Default)
Low Medium-
Low
Medium
High
High
(Default)
Increase (+10%) Cool CFM 610 770 900 1035 920 1080 1215 1385
Default Cool CFM 545 690 805 920 835 1000 1135 1255
Decrease (-10%) Cool CFM 465 620 720 810 750 890 1025 1145
The e󰀨ect of static pressure is included in air volumes shown.
The following control congurations are available. See Installation Instructions for details and DIP switch settings.
Heat Modes Available (Heating Blower Performance Table):
Single-stage thermostat:
- 35%, 70%, 100% input (three-stage) with time delays in-between
Two-stage thermostat:
- Variable Rate Capacity Mode - furnace automatically adjusts ring rate based on rst- and second-stage cycle times.
- W1 demand at 70% input, W2 demand at 100% input. No delay between stages.
Cool Mode Available (Cooling Blower Performance Table):
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan speeds are approximately 28% and 38% (DIP switch selectable) of the same second-stage COOL speed position minimum 250 cfm.
Lennox iHarmony® Zoning System Applications - Minimum blower speed is 250 cfm.

Page 6
BLOWER DATA
SLP99DF090XV48C BLOWER PERFORMANCE (less lter)
HEATING BLOWER PERFORMANCE - 0 through 0.8 in. w.g. External Static Pressure Range
Heating Adjust CFM Selections Heating Input Range and Blower Volume - CFM
35% 40% 50% 60% 70% 80% 90% 100%
Increase (+15%) Heat CFM 723 790 925 1060 1195 1329 1464 1599
Increase (+7.5%) Heat CFM 690 752 878 1004 1129 1255 1381 1507
Default Heat CFM 656 714 831 948 1064 1181 1297 1414
Decrease (-7.5% ) Heat CFM 601 654 761 867 974 1081 1188 1295
Decrease (-15% ) Heat CFM 545 593 690 787 884 981 1078 1175
The e󰀨ect of static pressure is included in air volumes shown.
The following control congurations are available. See Installation Instructions for details and DIP switch settings.
Heat Modes Available (Heating Blower Performance Table):
Single-stage thermostat:
- 35%, 70%, 100% input (three-stage) with time delays in-between
Two-stage thermostat:
- Variable Rate Capacity Mode - furnace automatically adjusts ring rate based on rst- and second-stage cycle times.
- W1 demand at 70% input, W2 demand at 100% input. No delay between stages.
Cool Mode Available (Cooling Blower Performance Table):
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan speeds are approximately 28% and 38% (DIP switch selectable) of the same second-stage COOL speed position minimum 250 cfm.
Lennox iHarmony® Zoning System Applications - Minimum blower speed is 380 cfm.
COOLING BLOWER PERFORMANCE - 0 through 1.0 in. w.g. External Static Pressure Range
Cooling Adjust CFM
Selections
Blower Speed Selections
First Stage Cool Speed - cfm Second Stage Cool Speed - cfm
Low Medium-
Low
Medium
High
High
(Default)
Low Medium-
Low
Medium
High
High
(Default)
Increase (+10%) Cool CFM 775 940 1100 1255 1120 1340 1535 1745
Default Cool CFM 690 875 975 1135 1000 1220 1425 1625
Decrease (-10%) Cool CFM 635 755 915 1025 920 1100 1270 1470

Page 7
BLOWER DATA
SLP99DF090XV60C BLOWER PERFORMANCE (less lter)
HEATING BLOWER PERFORMANCE - 0 through 0.8 in. w.g. External Static Pressure Range
Heating Adjust CFM Selections Heating Input Range and Blower Volume - CFM
35% 40% 50% 60% 70% 80% 90% 100%
Increase (+15%) Heat CFM 653 728 877 1027 1176 1326 1475 1625
Increase (+7.5%) Heat CFM 603 673 813 953 1092 1232 1372 1512
Default Heat CFM 553 618 748 878 1009 1139 1269 1399
Decrease (-7.5% ) Heat CFM 510 570 690 811 931 1051 1171 1292
Decrease (-15% ) Heat CFM 467 522 632 743 853 963 1074 1184
The e󰀨ect of static pressure is included in air volumes shown.
The following control congurations are available. See Installation Instructions for details and DIP switch settings.
Heat Modes Available (Heating Blower Performance Table):
Single-stage thermostat:
- 35%, 70%, 100% input (three-stage) with time delays in-between
Two-stage thermostat:
- Variable Rate Capacity Mode - furnace automatically adjusts ring rate based on rst- and second-stage cycle times.
- W1 demand at 70% input, W2 demand at 100% input. No delay between stages.
Cool Mode Available (Cooling Blower Performance Table):
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan speeds are approximately 28% and 38% (DIP switch selectable) of the same second-stage COOL speed position minimum 250 cfm.
Lennox iHarmony® Zoning System Applications - Minimum blower speed is 450 cfm.
COOLING BLOWER PERFORMANCE - 0 through 1.0 in. w.g. External Static Pressure Range
Cooling Adjust CFM
Selections
Blower Speed Selections
First Stage Cool Speed - cfm Second Stage Cool Speed - cfm
Low Medium-
Low
Medium
High
High
(Default)
Low Medium-
Low
Medium
High
High
(Default)
Increase (+10%) Cool CFM 1110 1265 1395 1600 1600 1750 1965 2130
Default Cool CFM 1000 1145 1275 1445 1445 1625 1805 1975
Decrease (-10%) Cool CFM 885 1060 1145 1265 1265 1445 1645 1805

Page 8
BLOWER DATA
SLP99DF110XV60C BLOWER PERFORMANCE (less lter)
HEATING BLOWER PERFORMANCE - 0 through 0.8 in. w.g. External Static Pressure Range
Heating Adjust CFM Selections Heating Input Range and Blower Volume - CFM
35% 40% 50% 60% 70% 80% 90% 100%
Increase (+15%) Heat CFM 811 906 1096 1286 1475 1665 1855 2045
Increase (+7.5%) Heat CFM 744 835 1017 1199 1380 1562 1744 1926
Default Heat CFM 677 764 938 1112 1285 1459 1633 1807
Decrease (-7.5% ) Heat CFM 626 707 869 1031 1193 1355 1517 1679
Decrease (-15% ) Heat CFM 575 650 800 950 1101 1251 1401 1551
The e󰀨ect of static pressure is included in air volumes shown.
The following control congurations are available. See Installation Instructions for details and DIP switch settings.
Heat Modes Available (Heating Blower Performance Table):
Single-stage thermostat:
- 35%, 70%, 100% input (three-stage) with time delays in-between
Two-stage thermostat:
- Variable Rate Capacity Mode - furnace automatically adjusts ring rate based on rst- and second-stage cycle times.
- W1 demand at 70% input, W2 demand at 100% input. No delay between stages.
Cool Mode Available (Cooling Blower Performance Table):
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan speeds are approximately 28% and 38% (DIP switch selectable) of the same second-stage COOL speed position minimum 250 cfm.
Lennox iHarmony® Zoning System Applications - Minimum blower speed is 450 cfm.
COOLING BLOWER PERFORMANCE - 0 through 1.0 in. w.g. External Static Pressure Range
Cooling Adjust CFM
Selections
Blower Speed Selections
First Stage Cool Speed - cfm Second Stage Cool Speed - cfm
Low Medium-
Low
Medium
High
High
(Default)
Low Medium-
Low
Medium
High
High
(Default)
Increase (+10%) Cool CFM 1090 1260 1395 1580 1580 1790 1990 2180
Default Cool CFM 965 1125 1285 1440 1440 1625 1845 2000
Decrease (-10%) Cool CFM 860 1030 1125 1270 1270 1470 1655 1845

Page 9
FIGURE 1
BURNER BOX ASSEMBLY
GAS VALVE
ACCESS PANEL
COMBUSTION AIR INDUCER
BLOWER
ACCESS
PANEL
BLOWER ASSEMBLY
(Variable Speed Blower
Motor Is Hidden)
BAG ASSEMBLY
CONTROL BOX
(includes variable capacity
integrated control,
transformer, circuit breaker
and door switch)
PRIMARY LIMIT
SLP99DFV PARTS ARRANGEMENT

Page 10
I-UNIT COMPONENTS
SLP99DFV unit components are shown in figure 1. The gas
valve, combustion air inducer and burners can be accessed
by removing the access panel. Electrical components are in
the control box (figure 2) found in the blower compartment.
CAUTION
Electrostatic discharge can affect elec
tronic components. Take precautions to
neutralize electrostatic charge by touch
ing your hand and tools to metal prior to
handling the control.
A-Control Box
1. Control Transformer (T1)
A transformer located in the control box provides power to
the low voltage section of the unit. Transformers on all mod
els are rated 40VA with a 120V primary and a 24V secon
dary.
2. Interlock Switch (S51)
An interlock switch rated 14A at 125VAC is wired in series
with line voltage. When the inner blower access panel is re
moved the unit will shut down.
FIGURE 2
CONTROL BOX SLP99DFV
SURELIGHT®
INTEGRATED
CONTROL TRANSFORMER
CIRCUIT
BREAKER
DOOR
INTERLOCK
SWITCH
3. Circuit Breaker (CB8)
A 24V circuit breaker is also located in the control box.
The switch provides overcurrent protection to the trans
former (T1). The breaker is rated 3A at 32V. If the current
exceeds this limit the breaker will trip and all unit opera
tion will shut down. The breaker can be manually reset by
pressing the button on the face. See figure 3.
FIGURE 3
CIRCUIT BREAKER CB8
PRESS TO RESET
WARNING
Shock hazard.
Disconnect power before servicing.
Integrated control is not field repairable. If control
is inoperable, simply replace entire control.
Can cause injury or death. Unsafe operation will re
sult if repair is attempted.
4. Integrated Control (A92)
SLP99DFV units are equipped with the Lennox SureLight®
variable-capacity integrated control. This control can be
used with a communicating thermostat as part of a commu
nicating system. The control can also operate with a con
ventional single or two-stage thermostat. The system con
sists of an ignition / blower control (figures 4 and 5) with
control pin designations in tables 1, 2 and ignitor. The con
trol provides gas ignition, safety checks and indoor blower
control with variable capacity rate gas heating. The furnace
combustion air inducer, gas valve and indoor blower are
controlled in response to various system inputs such as
thermostat signal, pressure and limit switch signal and
flame signal. The control features a seven-segment LED
display, indicating furnace status (including indoor blower)
and error codes. The LED flashes in single digits. For exam
ple using table 14 under LIMIT CODE, an “E” followed by
“2” followed by “5” followed by “0”, the limit switch circuit is
open. The control also has two 120 volt accessory terminals
(used for a humidifier and electronic air cleaner) rated at (1)
one amp each.