Haier GE APPLIANCES NF96US User manual

31-5000728 Rev. 0 10-22 GEA
NF96US
96% Upow/Horizontal Single Stage
Constant Torque Motor Gas Furnace
Service
Manual
READ CAREFULLY.
KEEP THESE INSTRUCTIONS.

Page 2 31-5000728 Rev. 0
SERVICE MANUAL
NF96US Gas Furnace - Upow/Horizontal
Table of Contents
Technical Specications - NF96US .............................3
Parts Arrangement.......................................................7
Electrical......................................................................8
Placement & Installation............................................21
Joint Cementing Procedure.......................................22
Venting Practices.......................................................23
Vent Piping Guidelines ..............................................24
Condensate Piping ....................................................40
Start-Up .....................................................................45
Heating System Service Checks ...............................46
Typical Operating Characteristics..............................50
Maintenance..............................................................51
Wiring Diagram..........................................................54
Troubleshooting: Heating Sequence of Operation ....55
Troubleshooting: Heating Sequence of Operation
(Continued)................................................................56
Troubleshooting: Cooling Sequence of Operation.....57
Troubleshooting: Continuous Fan / Accessories
Sequence of Operation..............................................58
This is a safety alert symbol and should never be ignored. When you see this symbol on labels or in manuals, be alert to
the potential for personal injury or death.
Electric shock hazard.
Can cause injury or death. Before attempting
to perform any service or maintenance,
turn the electrical power to unit OFF at
disconnect switch(es). Unit may have
multiple power supplies.
WARNING
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.
CAUTION
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.
WARNING

Page 3
31-5000728 Rev. 0
Technical Specications - NF96US
PHYSICAL AND ELECTRICAL DATA
Model Input
(Btuh)
Output
(Btuh)
AFUE
(ICS)
Nominal
Cooling
Capacity
Gas
Inlet
(in.)
Volts/
Hz/
Phase
Max.
Time
Delay
Breaker
or Fuse
Nominal
F.L.A.
Trans.
(V.A.)
Approx.
Shipping
Weight
(lbs.)
Upow/Horizontal
NF96U045S3B 44,000 42,000 96% 3 Ton 1/2 120-60-1 15 6.8 40 129
NF96U070S3B 66,000 63,000 96% 3 Ton 1/2 120-60-1 15 6.8 40 134
NF96U090S4C 88,000 85,000 96% 4 Ton 1/2 120-60-1 15 8.4 40 158
NF96U110S5C 110000 106000 96% 5 Ton 1/2 120-60-1 15 10.9 40 170
Note: For vent length and clearances to combustibles, please reference installation instructions.
MODEL NUMBER GUIDE
MAJOR/MINOR REVISION
CABINET WIDTH
B - 17.5”
C - 21”
D - 24.5”
NOMINAL CFM
3 - 1200 CFM
4 - 1600 CFM
5 - 2000 CFM
DESIGN VARIANT
S-ECM, 1 STAGE
BRAND
N - GE
PRODUCT
F - FURNACE, GAS
AFUE
96 = 96% EFFICIENCY
APPLICATION
U - UPFLOW/HORIZONTAL
HEATING INPUT (1000 BTU/HR)
45, 70, 90, 110
NNFF9696 UUSS55CCXXXX
110110

Page 4 31-5000728 Rev. 0
BLOWER PERFORMANCE DATA
NF96U045S3B PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
Air Volume / Watts at Various Blower Speeds
High Medium-High Medium Medium-Low Low
cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts
0.00 1460 335 1285 235 1190 170 910 85 870 75
0.10 1430 350 1260 245 1155 185 885 95 830 85
0.20 1405 365 1235 255 1125 200 860 105 800 90
0.30 1375 370 1205 265 1090 210 825 115 755 95
0.40 1350 380 1175 275 1055 215 780 125 710 105
0.50 1315 385 1145 285 1020 230 735 130 665 115
0.60 1245 375 1110 295 980 240 685 140 620 125
0.70 N/A N/A 1070 305 940 250 640 145 575 135
0.80 N/A N/A 1020 310 905 260 600 155 530 140
NF96U070S3B PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
Air Volume / Watts at Various Blower Speeds
High Medium-High Medium Medium-Low Low
cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts
0.00 1445 315 1315 215 1215 165 930 85 925 75
0.10 1445 335 1275 230 1170 180 905 94 860 80
0.20 1415 345 1240 240 1125 190 870 101 800 85
0.30 1380 355 1205 250 1090 200 830 109 760 95
0.40 1345 370 1175 265 1055 210 790 117 710 105
0.50 1315 385 1150 280 1020 220 735 129 665 115
0.60 1275 390 1110 290 985 230 685 137 625 125
0.70 1210 395 1075 300 950 240 640 146 565 130
0.80 N/A N/A 1030 305 915 250 595 148 535 135
NF96U090S4C PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
Air Volume / Watts at Various Blower Speeds
High Medium-High Medium Medium-Low Low
cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts
0.00 1765 375 1535 250 1410 180 1315 155 1155 115
0.10 1735 390 1500 260 1365 200 1270 165 1130 125
0.20 1700 405 1465 275 1330 215 1230 175 1095 135
0.30 1660 425 1435 290 1295 225 1195 190 1055 145
0.40 1640 435 1400 300 1265 235 1165 200 1010 155
0.50 1615 450 1370 315 1230 250 1125 215 965 165
0.60 1575 465 1340 325 1190 265 1080 230 925 180
0.70 1530 470 1305 340 1150 280 1045 235 885 190
0.80 N/A N/A 1260 345 1115 285 1000 245 845 195

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31-5000728 Rev. 0
NF96U110S5C PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
Air Volume / Watts at Di󰀨erent Blower Speeds
Bottom Return Air, Side Return Air with Optional Return Air Base, Return Air from Both
Sides or Return Air from Bottom and One Side.
Single Side Return Air − Air volumes in bold require eld fabricated transition to
accommodate 20 x 25 x 1 in. air lter in order to maintain proper air velocity.
High Med-High Medium Med-Low Low High Med-High Medium Med-Low Low
cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts
0.00 2220 655 1975 440 1800 325 1665 390 1050 180 2180 685 1910 460 1750 345 1660 285 1430 195
0.10 2185 680 1925 460 1750 345 1625 285 1440 200 2155 705 1885 480 1720 360 1610 295 1415 205
0.20 2150 705 1880 480 1710 365 1590 300 1390 220 2130 725 1855 495 1685 380 1565 305 1380 220
0.30 2110 720 1850 495 1680 380 1560 320 1350 230 2085 745 1825 510 1655 390 1535 325 1335 230
0.40 2080 735 1810 520 1650 405 1515 330 1310 245 2060 760 1795 530 1625 405 1495 340 1295 245
0.50 2045 755 1785 530 1610 415 1470 350 1265 255 2030 775 1765 545 1585 425 1450 355 1255 265
0.60 2010 775 1740 545 1575 430 1440 370 1220 270 1995 785 1725 565 1550 435 1420 370 1205 275
0.70 1980 790 1705 565 1525 450 1400 375 1170 280 1960 795 1690 575 1505 455 1385 385 1165 290
0.80 1950 795 1670 580 1485 460 1360 390 1140 293 1895 790 1650 590 1465 470 1335 395 1120 295

Page 6 31-5000728 Rev. 0
ACCESSORIES
System Accessory Kit Number Description
Natural to LP Kit (See Table 16)
11K50 1-Stage
11K45 High Altitude 1-Stage
Return Air Base
68W62 17.5" B Width
68W63 21.0" C Width
Flush Mount Termination
(90% Furnaces Only) (US Only) 51W11 2" & 3" Vent Version
Concentric Vent Kit
(90% Furnaces Only) (US Only)
71M80 1-1/2" Vent Version
69M29 2" Vent Version
60L46 3" Vent Version
Concentric Vent Kit
(90% Furnaces Only) (Canada Only)
44W92 1-1/2" and 2" Vent Version
44W93 3" Vent Version
Twinning Kit 16W72 Constant Torque Gas Furnace Twinning Kit
Note: For vent length and clearances to combustibles, please reference installation instructions.

Page 7
31-5000728 Rev. 0
Figure 1.
Parts Arrangement

Page 8 31-5000728 Rev. 0
Electrical
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
Electrostatic discharge can a󰀨ect electronic
components. Take precautions to
neutralize electrostatic charge by touching
your hand and tools to metal prior to
handling the control.
CAUTION
NF96US unit components are shown in Figure 1. The
combustion air inducer, gas valve and burners can be
accessed by removing the outer access panel. The blower
and control box can be accessed by removing the blower
access panel.
Control Box Components (Figure 2)
Unit transformer (T1) and integrated ignition control
(A92) are located in the control box. In addition, a door
interlockswitch (S51) is located in the control box.
Figure 2. Control Box
Transformer (T1)
A transformer located in the control box provides power
to the low voltage section of the unit. The transformers on
all models are rated at 40VA with a 120V primary and 24V
secondary.
Door Interlock Switch (S51)
A door interlock switch rated 14A at 120VAC is located
on the control box. The switch is wired in series with line
voltage. When the blower door is removed the unit will shut
down.
Circuit Breaker (CB8)
A 24V circuit breaker is also located in the control box. The
switch provides overcurrent protection to the transformer
(T1). The breaker is rated at 3A at 32V. If the current
exceeds this limit the breaker will trip and all unit operation
will shutdown. The breaker can be manually reset by
pressing the button on the face.
Integrated Ignition Control (A92)
Shock hazard.
Disconnect power before servicing.
Control is not eld repairable. If control is
inoperable, simply replace entire control.
Can cause injury or death. Unsafe
operation will result if repair is attempted.
WARNING
The hot surface ignition control system consisting of
an integrated control (Figure 3 with control terminal
designations in Table 1 through Table 3), sensor and
ignitor (Figure 5). The integrated control and ignitor work
in combination to ensure furnace ignition and ignitor
durability. The integrated control, controls all major furnace
operations. The integrated control also features a RED
LED for troubleshooting and two accessory terminals rated
at (1) one amp. See Table 4 for troubleshooting diagnostic
codes. The nitride ignitor is made from a non-porous, high
strength proprietary ceramic material that provides long life
and trouble free maintenance.
Pin # Function
1Combustion Air Inducer Line
2Ignitor Line
3Combustion Air Inducer Neutral
4Ignitor Neutral
Table 1. 4-Pin Terminal Designations
Pin # Function
1High Limit Output
2Not Used
324V Line
4Not Used
5Rollout Switch Out
624V Neutral
7High Limit Input
8Ground
9Gas Valve Common
10 Pressure Switch In
11 Rollout Switch In
12 Gas Valve Out
Table 2. 12-Pin Terminal Designations
Transformer
Circuit Breaker
Door Interlock
Switch
Integrated Control

Page 9
31-5000728 Rev. 0
1/4” Quick Connect Terminals
120HUM Humidier 120VAC
LINE 120VAC
XFMR Transformer 120VAC
CIRC Indoor Blower 120VAC
EAC Indoor Air Quality Accessory 120VAC
NEUTRALS Common 120VAC
HUM24 Humidier 24VAC
3/16” Quick Connect Terminals
COOL Cooling Tap 24VAC
HEAT Heating Tap 24VAC
FAN Continuous Blower 24VAC
PARK (no power) Park terminal for unused speed taps
FS Flame Sense
24 COM Common 24VAC
Table 3.
The integrated control is equipped with an LED light for troubleshooting. The diagnostic codes are listed in Table 4.
Red LED Flash Code2Diagnostic Codes / Status of Furnace
O󰀨 No power to control or board fault detected
Heartbeat1Normal Operation - Idle, Continuous Fan, Cool
Continuous Rapid Flash Call for Heat / Burner Operation
1Reverse Line Voltage Polarity
2Improper Earth Ground
3Burner failed to light, or lost ame during heat demand
4Low Flame Signal - check ame sensor
5Watchguard - burner failed to light, exceeded maximum number of retries or recycles
6Not Used
7Primary or Secondary Limit Open or Watchguard Mode - Limit Switch Open longer than 3 minutes
8Rollout Switch Open
9Pressure Switch failed to close or opened during heat demand
10 Watchguard - Pressure Switch opened 5 times during one heat demand
11 Pressure Switch stuck closed prior to activation of combustion air inducer
12 Flame Sensed without gas valve energized
13 Low Line Voltage
1 A ”Heartbeat” is indicated by a ”Slow Flash” - 1 sec on 1 sec o󰀨, repeating
2 Error codes are indicated by a ”Rapid Flash” - the LED ashes X times at 1/2 sec on 1/2 sec o󰀨, remains o󰀨 for 3 sec, then repeats
NOTE: Last 10 error codes are stored in memory including when power is shut o󰀨 to the unit. - To recall, press and release button,
most recent will be displayed rst, LED o󰀨 for 3 sec, then next error code is displayed, etc. To clear error codes, depress and
hold button longer than 5 seconds.
Table 4. Control Diagnostic Codes

Page 10 31-5000728 Rev. 0
Figure 3. Integrated Control
(Automatic Hot Surface Ignition System)
Electronic Ignition
On a call for heat the integrated control monitors the
combustion air inducer pressure switch. The control board
will not begin the heating cycle if the pressure switch is
closed (by-passed). Once the pressure switch is determined
to be open, the combustion air inducer is energized. When
the di󰀨erential in the pressure switch is great enough, the
pressure switch closes and a 15-second pre-purge begins.
If the pressure switch is not proven within 2-1/2 minutes,
the integrated control goes into Watchguard-Pressure
Switch mode for a 5-minute re-set period.
After the 15-second pre-purge period, the ignitor warms
up for 20 seconds during which the gas valve opens at
19 seconds for a 4-second trial for ignition. The ignitor
remains energized for the rst 3 seconds during the 4
second trial. If ignition is not proved during the 4-second
period, the integrated control will try four more times with
an inter purge and warm-up time between trials of 35
seconds. After a total of ve trials for ignition (including the
initial trial), the integrated control goes into Watchguard-
Flame Failure mode. After a 60-minute reset period, the
integrated control will begin the ignition sequence again.
Fan Time Control
Heating Fan On Time
The fan on time of 30 seconds is not adjustable.
Heating Fan O󰀨 Time
Fan o󰀨 time (time that the blower operates after the heat
demand has been satised) can be adjusted by moving
the jumper to a di󰀨erent setting. The unit is shipped with
a factory fan o󰀨 setting of 90 seconds. For customized
comfort, monitor the supply air temperature once the heat
demand is satised. Note the supply air temperature at the
instant the blower is de-energized.
Adjust the fan-o󰀨 delay to achieve a supply air temperature
between 90° - 110° at the instant the blower is de-energized.
(Longer delay times allow for lower air temperature, shorter
delay times allow for higher air temperature). See Figure 4.
Cooling Fan On Time
The fan on time is 2 seconds and is not adjustable.
Cooling Fan O󰀨 Time
The control has a 45 second fan o󰀨 delay after cooling
demand has been met. This delay is factory set and not
adjustable.
60 90
120
180
60 90
120
180
60 90
120
180
60 90
120
180
Figure 4. Heat Fan-O󰀨 Time in Seconds
Heating Components
Combustion air inducer (B6), primary limit control (S10),
ignitor, burners, ame rollout switch (S47), gas valve
(GV1), combustion air pressure switch (S18), and heat
exchangers are located in the heating compartment. The
heating compartment can be accessed by removing the
outer access panel.
Ignitor (Figure 5)
NF96US units use a nitride ignitor made from a proprietary
ceramic material. To check ignitor, measure its resistance
and voltage. A value of 39 to 70 ohms indicates a good
ignitor. Voltage to the ignitor should be 102 - 132VAC. See
Figure 9 for resistance and voltage checks.
RED LED RECALL BUTTON BLOWER OFF DELAY
To adjust fan-o󰀨 timing, reposition jumper across pins to
achieve desired setting.
60 Second
o󰀨 time
90 Second
o󰀨 time
120 Second
o󰀨 time
180 Second
o󰀨 time
JUMPER POSITION HEAT OFF DELAY
PIN1 PIN2 60
PIN2 PIN3 90
PIN3 PIN4 120
PIN4 PIN5 180
NO JUMPER 180

Page 11
31-5000728 Rev. 0
Figure 5. Burner Box Assembly
Gas Valve
Burner Box Front
Rollout Switch(s)
Flame Sensor
Ignitor
Burner Assembly
Flame Rollout Switches (Figure 5)
Flame rollout switches S47 are SPST N.C. high temperature
limits located on the left and right of the front buner box
plate. S47 is wired to the burner ignition control A92. When
either of the switches sense ame rollout (indicating a
blockage in the combustion passages), the ame rollout
switch trips, and the ignition control immediately closes the
gas valve. Switch S47 in all NF96US units is factory preset
to open at 210 F + 12 F (99 C + 6.7 C) on a temperature rise.
All ame rollout switches are manual reset. See ash code
8 in Table 4 for troubleshooting.
Flame Sensor (Figure 5)
A ame sensor is located on the left side of the burner
support. The sensor is mounted on the front burner box
plate and the tip protrudes into the ame envelope of the
leftmost burner. The sensor can be removed for service
(use steel wool only to clean) without removing any part of
the burners. During operation, ame is sensed by current
passed through the ame and sensing electrode. The
ignition control allows the gas valve to remain open as long
as ame signal is sensed.
NOTE: The NF96US is polarity sensitive. Make sure that
the furnace is wired correctly and is properly grounded.
A microamp DC meter is needed to check the ame signal
on the integrated control.
Flame (microamp) signal is an electrical current which
passes from the integrated control to the sensor during
unit operation. Current passes from the sensor through the
ame to ground to complete a safety circuit.
Heat Exchanger (Figure 6)
NF96US units use an aluminized steel primary and
stainless steel secondary heat exchanger assembly. Heat
is transferred to the air stream from all surfaces of the
heat exchanger. The shape of the heat exchanger ensures
maximum e󰀩ciency.
The combustion air inducer pulls fresh air through the
burner box. This air is mixed with gas in the burners. The
gas / air mixture is then burned at the entrance of each
clamshell. Combustion gases are then pulled through the
primary and secondary heat exchangers and exhausted
out the exhaust vent pipe.

Page 12 31-5000728 Rev. 0
Primary Limit Control (Figure 6)
Primary limit (S10) used on NF96US units is located in the
heating vestibule panel. When excess heat is sensed in the
heat exchanger, the limit will open. Once the limit opens,
the furnace control energizes the supply air blower and
de-energizes the gas valve. The limit automatically resets
when unit temperature returns to normal. The switch is
factory set and cannot be adjusted. For limit replacement
remove wires from limit terminals, remove mounting
screws, rotate limit switch 90 degrees and slowly remove
from the vestibule panel. Install replacement limit with
same care. See ash code 7 in Table 4 for troubleshooting
if limit switch opens during operation.
Figure 6. Primary Limit Location and Heat Exchanger
Installlimit face down
Gas Valve (Figure 7)
The NF96US uses an internally redundant valve to assure
safety shut-o󰀨. If the gas valve must be replaced, the same
type valve must be used.
24VAC terminals and gas control switch are located on top
of the valve. All terminals on the gas valve are connected to
wires from the ignition control. 24V applied to the terminals
opens the valve.
Inlet and outlet pressure taps are located on the valve. A
manifold adjustment screw is also located on the valve. An
LP/Propane changeover kit is available.
Figure 7. Gas Valve
GAS VALVE SHOWN IN ON POSITION
MANIFOLD
PRESSURE
OUTLET
PORT
INLET
PRESSURE
PORT
MANIFOLD PRESSURE
ADJUSTMENT SCREW
(under barbed fitting)
To Measure Flame Signal - Integrated Control:
Use a digital readout meter capable of reading DC
microamps. See Figure 8 for ame signal check.
1. Set the meter to the DC amps scale.
2. Turn o󰀨 supply voltage to control.
3. Remove sensor wire from integrated control.
4. Connect (-) lead to ame sensor wire.
5. Connect (+) lead to Terminal FS on integrated control.
6. Turn supply voltage on and close thermostat contacts
to cycle system.
7. When main burners are in operation for two minutes,
take reading.

Page 13
31-5000728 Rev. 0
Figure 8. Measuring Flame Signal
Flame Signal In Microamps
Normal Low Drop Out
1.50.5- 1.4 0.4
Set Dial to DC MicroAmps
(+)
Multi−Meter
(+)
(+) To Control
Sensor Terminal
(−) To Flame
Terminal
Flame Sensor
Terminal
Flame Sensor
Wire
Intergrated
Control
Remove sensor from integrated
control and connect alligator clip
(−) to flame sensor lead.
Remove sensor from integrated
control and connect alligator clip
(+) to terminal on control.

Page 14 31-5000728 Rev. 0
Figure 9.
Test 1
Check ignitor circuit for correct resistance.
Remove 4-pin plug from control.
Check ohms reading across terminals 2 and 4.
Reading should be between 39 and 70 ohms. If
value is correct, this is the only test needed.
If the reading on the meter is not correct, (0 or
infinity) then a second test is needed.
Test 2
Check ignitor for correct resistance.
Seperate the 2-pin jack-plug near the manifold and check
resistance of ignitor at the plug. Reading should be
between 39 and 70 ohms. If the reading is correct, then
the problem is with the wiring between the jack-plug and
the control. If reading is not correct, the issue is the ignitor.
Test 3
Check ignitor for correct voltage
Insert meter probes into terminals 2 and 4 (use small
diameter probes in order not to damage plug).
Check voltage during 20 second ignitor warm up period.
Voltage should read 120 volts + 10%. If voltage reads below
these values, check for correct supply voltage to furnace.
Multi−Meter
(set to ohms)
Multi−Meter
(set to ohms)
Multi−Meter
(set to VAC)

Page 15
31-5000728 Rev. 0
Combustion Air Inducer (B6) & Cold End Header Box
All NF96US units use a combustion air inducer to move
air through the burners and heat exchanger during heating
operation. The blower uses a shaded pole 120VAC motor.
The motor operates during all heating operation and is
controlled by integrated control A92. Blower operates
continuously while there is a call for heat. The integrated
control will not proceed with the ignition sequence until
combustion air inducer operation is sensed by the proving
switches.
The combustion air inducer is installed on the cold end
header box. The cold end header box is a single piece made
of hard plastic. The box has an internal channel where the
combustion air inducer creates negative pressure at unit
start up. The channel contains an orice used to regulate
ow created by the combustion air inducer. The box has
pressure taps for the combustion air inducer pressure
switch hoses. The pressure switch measures the pressure
across the combustion air inducer orice or di󰀨erence in
the channel and the box. If replacement is necessary the
gaskets used to seal the box to the vestibule panel and the
combustion air inducer to the box, must also be replaced.
Combustion Air Pressure Switch (Figure 10)
NF96US series units are equipped with a di󰀨erential
pressure switch located on the cold end header box. The
switch monitors across the combustion air inducer orice
to insure proper ow through the heat exchanger.
The switch is a SPST N.O. pressure switch electrically
connected to the integrated control. The purpose of the
switch is to prevent burner operation if the combustion air
inducer is not moving enough air for proper combustion.
Figure 10. Pressure Switch
On start-up, the switch monitors whether the combustion
air inducer is operating. It closes a circuit to the integrated
control when the di󰀨erence in pressure across the
combustion air inducer orice exceeds a non-adjustable
factory setting. If the switch does not successfully sense
the required di󰀨erential, the switch cannot close and the
furnace cannot operate. If the ue or air inlet become
obstructed during operation, the switch senses a loss of
pressure di󰀨erential and opens the circuit to the integrated
control. If the condensate line is blocked, water will back
up into the header box and reduce the pressure di󰀨erential
across the switch. The pressure switch opens if the
di󰀨erential drops below the set point. See Table 5.
Checks of pressure di󰀨erential can aid in troubleshooting.
When measuring the pressure di󰀨erential, readings should
be taken at the pressure switch. See Figure 11 and Table 6.
Lack of di󰀨erential usually indicates problems in the intake
or exhaust piping, but may indicate problems in the heat
exchanger, condensing coil, header boxes, combustion
inducer or other components.
Unit
Altitude (ft.)
0 - 4500
Set Point “w.c.
045 -0.65”
070 -0.90”
090 -0.90”
110 -0.90”
NOTE: Set point is factory set and non-adjustable
Table 5.

Page 16 31-5000728 Rev. 0
Figure 11. Measuring Pressure Di󰀨erential
To Cold End Header Box
Field Provided Tubing
To Pressure Switch
To Cold End Header Box
1 - Remove thermostat demand and allow unit to
cycle off.
2 - Install a tee in the negative (-) line (red and black tubing
or red tubing) and a tee in the positive (+)line (black
tubing) running from the pressure switch to the cold
end header box.
3 - Install a manometer with hose from the negative (-)
side of the manometer to the tee installed in the
negative (-) line and with hose from the positive (+)
side of the manometerto the tee in the positive (+)
line.
NOTE -
tive. However the (+) port reads less negative pressure
than the (-) port.
4 - Operate unit and observe manometer reading.
Readings will change as heat exchanger warms.
a. Take one reading immediately after start‐up.
b. Take a second reading after unit has reached
steady state (approximately 5 minutes). This will be
the pressure differential.
The pressure differential should be greater
than those listed in table 7.
5 - Remove thermostat demand and allow to cycle off.
6 - Remove manometer and tee's. Reinstall combustion
air sensing hoses to the pressure switch.
Black Tubing
(positive +)
Red and Black Tubing
or Red Tubing
(negative -)
“+”
High
“-”
Low

Page 17
31-5000728 Rev. 0
Problem Corrective Action
Pressure switch stuck closed Check that the pressure switch is open without the combustion air inducer
operating. Replace if defective.
Pressure switch does not close due to obstruction in
vent pipe
Check for restricted vent. Remove all blockage.
Check for proper vent sizing. See Table 10A through Table 10F.
Pressure switch does not close due to incorrect
routing of the pressure switch tubing
Check that the pressure switch tubing is correctly routed. Correctly route
pressure switch line.
Pressure switch does not close due to obstructions in
the pressure switch line Remove any obstructions from the the pressure switch line and/or taps
Pressure switch tubing damaged Check pressure switch tubing for leaks. Replace damaged tubing if
necessary.
Condensate in pressure switch tubing Check pressure switch tubing for condensate. Remove condensate from
tubing.
Pressure switch does not close due to a low
di󰀨erential pressure across the pressure switch
Check the di󰀨erential pressure across the pressure switch.
Check for restricted inlet vent. Remove all blockage.
Check for proper vent sizing and run length. See Table 10A through Table
10F.
Wrong pressure switch installed in the unit, or
pressure switch is out of calibration
Check that the correct pressure switch is installed in the unit. Replace
pressure switch if necessary.
Miswiring of furnace or improper connections at
pressure switch
Check for correct wiring and loose connections. Correct wiring and/or replace
any loose connections.
Pressure switch failure If all the above modes of failure have been checked, the pressure switch
may have failed. Replace pressure switch and determine if unit will operate.
Damaged condensate trap Check trap for any cracks or damage and replace if necessary.
Cold end header box does not drain properly Check that the furnace is set properly with a slight tilt (0 - 1/2”) towards the
front if necessary. See furnace installation instruction.
Air leakage around the combustion air inducer gasket Check gasket and replace if necessary.
Air leakage around the cold end header box gasket Check gasket and replace if necessary.
Damaged cold end header box tubing Check tubing and replace if necessary.
Table 6. Pressure Switch Troubleshooting Guide
Figure 12.
DEMAND
CAI
GAS VALVE
15
ON
OFF
38
IGNITOR
34
1
Pre -Purge Ignitor Warm-up Trial for
Ignition Post
Purge
5 SEC80
*Blower on time will be 30 seconds after flame is sensed. Blower off time will depend on “OFF TIME” Setting.
INDOOR BLOWER
Blower “On”*
Delay

Page 18 31-5000728 Rev. 0
Blower Compartment
Each blower is statically and dynamically balanced as
an assembly before installation in the unit.
IMPORTANT
NF96US units are equipped with a constant torque ECM
motor. It has a DC motor coupled to an electronic control
module both contained in the same motor housing. The
motor is programmed to provide constant torque at each of
the ve selectable speed taps. Each tap requires 24 volts
to energize.
Input Voltage Requirements
The circuit is designed to be operated with AC voltage. To
enable a tap requires 12 to 33VAC. Expected current draw
will be less than 20mA.
Troubleshooting the Motor
Troubleshooting the motor is an easy process. Follow
steps below.
1. Shut o󰀨 power to unit.
2. Remove input plugs P48 and P49 from motor. See
Figure 16 for troubleshooting procedure.
If correct voltage is present in tests 1 and 2 and motor is
not operating properly, replace motor. The motor is not eld
repairable.
If replacing the indoor blower motor or blower wheel is
necessary, placement is critical. The blower wheel must
be centered in the blower housing as shown in Figure 13.
When replacing the indoor blower motor the set screw
must be aligned and tightened with the motor shaft as
shown in Figure 14.
Secondary Limit Controls
The secondary limit is located in the blower compartment
on the back side of the blower housing. See Figure 15.
When excess heat is sensed in the blower compartment,
the limit will open. If the limit is open, the furnace control
energizes the supply air blower and closes the gas valve.
The limit automatically resets when unit temperature
returns to normal. The secondary limit cannot be adjusted.
Figure 13. Blower Wheel Replacement
Figure 14.
Set Screw
Housing Hub
ALIGN AND TIGHTEN SET SCREW WITH
FLAT SIDE OF MOTOR SHAFT
Motor
Shaft
Figure 15. Secondary Limit Control
Secondary Limits
Center Blower Wheel
in Blower Houseing

Page 19
31-5000728 Rev. 0
Figure 16.
1
2
3
4
5
C
L
G
N
Multi−Meter
(set to VAC)
P48
P49
120 120
Turn on power to unit. Check for 120 volts across terminals
“L” and “N” on input plug P48. If voltage is present continue
upstream of plug P48. Proceed to test 3.
1
2
3
4
5
C
L
G
N
Multi−Meter
(set to VAC)
P48
P49 24
Switch thermostat to CONTINUOUS FAN MODE. Check for
24 volts across terminal “C” on input plug P48and speed tap
used for continuous fan. (1, 2, 3, 4 or 5) on input plug P49. If
24 volts is not present problem may be up stream of plug P49.
Proceed to test 4.
Multi−Meter
(set to VAC)
120 120
24
Multi−Meter
(set to VAC)
problem is with the harness. If voltage is not present,
problem may be may be with the integrated control.
Check for 120 volts across terminals “CIRC” and “Neutrals”
on the integrated control. If voltage is present, problem is
with the harness. If voltage is not present problem may be
may be with the integrated control.
Test 1
Test 2
Test 3 (if necessary)
Test 4 (if necessary)
to test 2. If voltage is not present, problem may be
Check for 24 volts across terminals “24 COM” and “FAN”
terminals on the integrated control. If voltage is present,

Page 20 31-5000728 Rev. 0
Testing the Motor (Figure 17)
If any motor fails the below tests, the motor is defective
and must be replaced.
1. Using an ohmmeter check the resistance from any
one of the motor connector pins to the aluminum end
plate of the motor. This resistance should be greater
than 100k ohms.
2. Check the resistances between each of the three motor
connector pins. These should all read approximately
the same resistance within an ohm.
3. Check to see if the blower wheel spins freely.
Figure 17. Motor Test
Scale Measurement Range in Words ohms
2 M two megohms - two million ohms 0 - 2,000,000
200 K two hundred kil-ohms -
two hundred thousand ohms 0 - 200,000
20 K twenty kilo-ohms -
twenty thousand ohms 0 - 20,000
2 K two kilo-ohms -
two-thousand ohms 0 - 2,000
200 two hundred ohms 0 - 200
Figure 18. Drip Loop
Back of Control
Module
Drip Loop
Connector
Orientation
Between 4 and 8
O’clock