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SERVICE AND TECHNICAL SUPPORT MANUAL

Gas Furnace: N9MSB

Specifications  subject to change without notice.

16

440 04 4413 03

Troubleshooting

Refer to the service label. (See 

Figure 14

—Service Label)

The Troubleshooting Guide 

 Flow Chart (See 

Figure 16

) can

be a useful tool in isolating furnace operation problems.

Beginning with the word “Start,” answer each question and

follow the appropriate arrow to the next item.
The Guide 

 Flow Chart will help to identify the problem or

failed component. After replacing any component, verify correct

operation sequence.

Proper instrumentation is required to service electrical controls.

The control in this furnace is equipped with a Status Code LED

(Light

Emitting  Diode) to aid in installation, servicing, and

troubleshooting. Status codes can be viewed at the indicator in

blower door. The green furnace control LED is either ON

heartbeat, off or a code composed of 1 or 2 digits. The first digit

is the number of short flashes, the second digit is the number of

long flashes.

Figure 7

Heating and Cooling Application Wiring Diagram with Single

Stage Thermostat

115-V FIELD-

SUPPLIED

DISCONNECT

AUXILIARY
J-BOX

24-V

TERMINAL

BLOCK

THREE-WIRE

HEATING-ONLY

FIVE WIRE

NOTE 1

NOTE 2

FIELD-SUPPLIED
DISCONNECT

CONDENSING
UNIT

TWO
WIRE

FURNACE

C
O
N

T

R
O

L

R

G

COM

W

C

R

G

Y

GND

GND

FIELD 24-V WIRING
FIELD 115-, 208/230-, 460-V WIRING
FACTORY 24-V WIRING
FACTORY 115-V WIRING

208/230- OR
460-V
THREE
PHASE

208/230-V
SINGLE
PHASE

BLOWER DOOR SWITCH

WHT

BLK

WHT

BLK

NOTES:

Connect Y-terminal in furnace as shown for proper blower operation.
Some thermostats require a "C" terminal connection as shown.
If any of the original wire, as supplied, must be replaced, use
same type or equivalent wire.

W

Y

GND

THERMOSTAT
TERMINALS

1.
2.
3.

A11387

For an explanation of status codes, refer to service label

located on blower door or 

Figure 14

, and the troubleshooting

guide which can be obtained from your distributor.

Retrieving Stored Fault Codes

NOTE

:  Fault codes cannot be retrieved if a thermostat signal

(24-V on W, Y, G, etc.) is present, or if any delays such as
blower off-delays are active.
The stored status codes will NOT be erased from the control

memory when 115- or 24-V power is interrupted. See the

Service Label (See 

Figure 14

) for more information. The most

recent fault code may be retrieved as follows:

1. Leave 115-V power connected to furnace.
2. Observe the status LED through the blower door (the

lower door on upflow applications) indicator. Refer to the

Service Label (See 

Figure 14

) to interpret the LED.

3. Remove the Main/Control door (the upper door on upflow

installations).

4. BRIEFLY disconnect and reconnect ONE of the main

limit wires.

5. The LED will flash the last stored fault code. Refer to the

Service Label (See 

Figure 14

) to interpret the LED.

6. A component test sequence will follow.
7. Reinstall the Main/Control door.

Component Self

Test 

NOTE

:  The furnace control component test allows all

components to run for a short time; except the gas valve and
humidifier terminal HUM 24 VAC are not energized. The EAC

terminal is energized when the blower is energized. The HUM
terminal is energized when the inducer is energized. This
feature helps diagnose a system problem in case of a

component failure. The component test feature will not operate
if any thermostat signal is present at the control and not until all
time delays are completed.

To begin Component Self

Test:

1. Remove blower access door.
2. Disconnect the thermostat R lead from furnace control.
3. Manually close blower door switch.

Caution must be taken when manually closing this switch for

service purposes.

ELECTRICAL SHOCK HAZARD

Failure to follow this warning could result in personal

injury, or death.
Blower access door switch opens 115

V power to

control. No component operation can occur unless

switch is closed. Caution must be taken when

manually closing this switch for service purposes.

!

WARNING

4. For approximately 2 sec, short (jumper) the C terminal on

control to the TEST/TWIN 3/16—in. (5 mm)

quick-connect terminal on control until the LED goes off.

Remove jumper from terminals. (See 

Figure 4

)

NOTE

:  If TEST/TWIN and C terminals are jumpered longer

than 2 sec, LED will flash code 10 and ignore component test

request.
Component test sequence is as follows:

a. LED will display previous status code 4 times.
b. Inducer motor starts and continues to run until Step f of

component test sequence.

Summary of Contents for N9MSB

Page 1: ...ls The signal word WARNING is used throughout this manual in the following manner Safety alert symbol When you see this symbol on the unit and in instructions or manuals be alert to the potential for personal injury TABLE OF CONTENTS START UP CHECK SHEET FOR PSC MOTOR 3 START UP ADJUSTMENT AND SAFETY CHECK 4 PRIME CONDENSATE TRAP WITH WATER 4 PURGE GAS LINES 4 ADJUST TEMPERATURE RISE 10 ADJUST BLO...

Page 2: ...death WARNING signifies hazards which could result in personal injury or death CAUTION is used to identify unsafe practices which may result in minor personal injury or product and property damage NOTE is used to highlight suggestions which will result in enhanced installation reliability or operation WARNING PERSONAL INJURY AND OR PROPERTY DAMAGE HAZARD Failure to carefully read and follow this w...

Page 3: ...eam of Furnace Drip Leg Gas Valve turned ON Type of Gas Natural Propane Filter Type and Size Check in box the Blower OFF Delay Jumper Heating Position for Fan Time OFF Setting 1 and 2 2 and 3 3 and 4 5 and 6 90 120 150 180 Calculated Input BTU Rate See Checks and Adjustments Section Heating Check Measured Line Pressure During Heat Measured Manifold Pressure Heat Temperature of Supply Air Heat Temp...

Page 4: ...ON Before operating furnace check flame rollout manual reset switch for continuity If necessary press button to reset switch EAC 115vac terminal is energized whenever blower operates HUM 24vac terminal is only energized the draft inducer is energized in heating Prime Condensate Trap with Water CARBON MONOXIDE POISONING HAZARD Failure to follow these warnings could result in personal injury or deat...

Page 5: ... gas heating values Refer to the instructions provided in the factory specified Propane conversion kit for instructions for setting gas manifold pressures for Propane applications In the USA the input rating for altitudes above 2000 ft 610 M must be reduced by 2 percent for each 1000 ft 305 M above sea level refer to Table 1 The natural gas manifold pressures in Table 3 adjust for BOTH altitude an...

Page 6: ...ometer to the inlet pressure tap on gas valve 4 Turn on furnace power supply 5 Turn gas supply manual shutoff valve to ON position 6 Turn furnace gas valve switch to ON position 7 Jumper R and W thermostat connections at the furnace control board 8 When main burners ignite confirm inlet gas pressure is between 4 5 in w c 1125 Pa and 13 6 in w c 3388 Pa 9 Remove jumper across thermostat connections...

Page 7: ...lution and note reading The 2 or 5 cubic feet dial provides a more accurate measurement of gas flow e Refer to Table 2 for cubic ft of gas per hr f Multiply gas rate cu ft hr by heating value Btuh cu ft to obtain input If clocked rate does not match required input from Step 1 increase manifold pressure to increase input or decrease manifold pressure to decrease input Repeat steps b through e until...

Page 8: ...FORMER 24 VAC CONNECTIONS P2 HOT SURFACE IGNITOR HSI INDUCER MOTOR IND CONNECTOR 115 VAC L1 LINE VOLTAGE CONNECTION SPARE1 COM BLUE 115 VAC L2 NEUTRAL CONNECTIONS 24 V THERMOSTAT TERMINALS HUMIDIFIER TERMINAL 24 VAC 0 5 AMP MAX 3 AMP FUSE LED OPERATION DIAGNOSTIC LIGHT 24VAC RED BLOWER SPEED SELECTION TERMINALS HUM XFMR HUMIDIFIER TERMINAL 115 VAC 120 180 90 150 SPARE2 J2 JUMPER J2 HUM 24VAC BLW S...

Page 9: ... 300 21 171 343 857 62 58 116 290 22 164 327 818 64 56 112 281 23 157 313 783 66 54 109 273 24 150 300 750 68 53 106 265 25 144 288 720 70 51 103 257 26 138 277 692 72 50 100 250 27 133 267 667 74 48 97 243 28 129 257 643 76 47 95 237 29 124 248 621 78 46 92 231 30 120 240 600 80 45 90 225 31 116 232 581 82 44 88 220 32 113 225 563 84 43 86 214 33 109 218 545 86 42 84 209 34 106 212 529 88 41 82 2...

Page 10: ...3 42 3 4 42 3 5 42 3 6 3001 800 43 3 8 42 3 2 42 3 3 42 3 4 915 825 43 3 6 43 3 7 43 3 8 42 3 2 850 44 3 8 43 3 5 43 3 6 43 3 7 875 44 3 6 44 3 7 43 3 4 43 3 5 4000 900 44 3 4 44 3 5 44 3 7 44 3 8 1219 925 44 3 2 44 3 4 44 3 5 44 3 6 950 44 3 1 44 3 2 44 3 3 44 3 4 750 42 3 3 42 3 4 42 3 5 42 3 6 4001 775 43 3 7 43 3 8 42 3 3 42 3 4 1220 800 43 3 5 43 3 6 43 3 7 43 3 8 825 44 3 8 43 3 4 43 3 5 43 ...

Page 11: ...ading Leaving blower door off will result in incorrect temperature measurements due to possible changes in duct static pressure and airflow FURNACE DAMAGE HAZARD Failure to follow this caution may result in S Overheating the heat exchangers or condensing flue gases in heat exchanger areas not designed for condensate S Shortened furnace life S Component damage Temperature rise must be within limits...

Page 12: ...se terminals R and W The thermostat anticipator should NOT be in the circuit while measuring current 1 Remove thermostat from sub base or from wall 2 Connect an amp meter across the R and W sub base terminals or R and W wires at wall 3 Record amp draw across terminals when furnace is in low heat and after blower starts 4 Set heat anticipator on thermostat per thermostat instructions and install on...

Page 13: ... Verify that there are no unsealed openings in the blower shelf or casing 5 Verify that the blower lower door in upflow position and control Main or upper door in upflow position doors are properly installed 6 Verify that the Status LED heartbeat bright dim If not check that the power supply is energized and that the blower door is secure See Figure 14 to interpret diagnostic codes 7 Cycle test fu...

Page 14: ...1665 1640 1595 1545 1485 1410 1330 1235 1135 Orange 3 5 397 1485 1470 1455 1430 1390 1340 1280 1205 1120 1035 Blue 3 2 5 426 1120 1110 1100 1090 1065 1035 990 935 870 805 Red 3 2 0 433 940 920 910 890 865 830 790 745 690 625 1002116 SIDE BOTTOM Black 4 0 373 1715 1660 1610 1555 1490 1420 1340 1245 1150 1065 Yellow 3 3 5 379 1535 1480 1435 1380 1325 1260 1180 1095 1010 910 Blue 3 3 0 367 1300 1255 ...

Page 15: ...blower is located below the combustion and controls section of the furnace and conditioned air is discharged upward Since this furnace can be installed in any of the 4 positions shown in Figure 6 you must revise your orientation to component location accordingly Figure 6 Multipoise Orientations A93041 Electrical Controls and Wiring Pressure Switches Each pressure switch is labeled with the referen...

Page 16: ... are active The stored status codes will NOT be erased from the control memory when 115 or 24 V power is interrupted See the Service Label See Figure 14 for more information The most recent fault code may be retrieved as follows 1 Leave 115 V power connected to furnace 2 Observe the status LED through the blower door the lower door on upflow applications indicator Refer to the Service Label See Fi...

Page 17: ...ace with filter or filtration device access doors removed WARNING CUT HAZARD Failure to follow this caution may result in personal injury Sheet metal parts may have sharp edges or burrs Use care and wear appropriate protective clothing safety glasses and gloves when handling parts and servicing furnaces CAUTION The minimum maintenance on this furnace is as follows 1 Check and clean air filter each...

Page 18: ...teps a through e g Tighten all clamps 15 lb in See Figure 8 for steps 5 through 14 5 Remove screws securing blower assembly to blower shelf and slide blower assembly out of furnace Detach ground wire and disconnect blower motor harness plugs from blower motor NOTE Blower wheel is fragile Use care 6 Clean blower wheel and motor by using a vacuum with soft brush attachment Be careful not to disturb ...

Page 19: ...supply and cycle furnace through one complete heating cycle Verify the furnace temperature rise as shown in Adjustments Section Adjust temperature rise as shown in Adjustments Section Cleaning Burners and Flame Sensor The following items must be performed by a qualified service technician If the burners develop an accumulation of light dirt or dust they may be cleaned by using the following proced...

Page 20: ... Figure 10 and Figure 11 Figure 10 Igniter Position Top View A11405 2 1 2 in 64 4 1 1 4 in 31 8 Figure 11 Igniter Position Side View L12F041 2ïin 2 5 mm 3 8ïin 3 16ïin 0 8 ï1 5 mm 50 mm 9 6 mm 4 6 mm 1 10ïin 1 32 ï 1 16ïin 9 Attach the wires to the roll out switches 10 Align the burner assembly with the openings in the primary cell inlet panel and attach the burner assembly to the cell panel 11 Co...

Page 21: ...rt on collect box and the trap with a small wire Shake any water out of the tube 13 Reconnect relief tube to trap and collector box ports Cleaning Condensate Drain and Trap NOTE If the condensate trap is removed a new gasket between the trap and collector box is required Verify a condensate trap gasket is included in the service kit or obtain one from your local distributor 1 Disconnect power at e...

Page 22: ...y restrict flow of combustion products 8 Reverse items 6 through 1 for reassembly 9 Refer to furnace wiring diagram and reconnect wires to flame rollout switch gas valve igniter and flame sensor 10 Turn on gas and electrical supplies to furnace 11 Check furnace operation through two complete heat operating cycles Look at burners Burner flames should be clear blue almost transparent See Figure 13 F...

Page 23: ...the funnel tube Antifreeze should run through the collector box overfill condensate trap and flow to an open drain 8 Replace the rubber plug in the port on the collector box 9 Remove the middle unused rubber plug from the port on the collector box opposite the condensate trap See Figure 1 10 Repeat Steps 5 through 8 11 If a condensate pump is used check with pump manufacturer to verify pump is saf...

Page 24: ...SERVICE AND TECHNICAL SUPPORT MANUAL Gas Furnace N9MSB Specifications subject to change without notice 24 440 04 4413 03 Figure 14 Service Label 338310 2 Rev F ...

Page 25: ...SERVICE AND TECHNICAL SUPPORT MANUAL Gas Furnace N9MSB Specifications subject to change without notice 440 04 4413 03 25 Figure 15 Wiring Diagram 339241 2 Rev A ...

Page 26: ...equence Gas valve and humidifier will not be turned on Inducer motor will start and remain on until the end of the blower test then off The following components are on for 10 15 seconds each individually hot surface igniter blower speeds FAN if present HEAT COOL Was there a previous status code Go to section below for the flashed status code Does the control respond to W Y1 Y Y2 and G 24V thermost...

Page 27: ...ponent test Does the igniter glow orange white by the end of the 15 second warm up period Unplug igniter harness from control and repeat component test Check for 115V between connector P2 HSI and NEUTRAL L2 on the control Was 115V present for the 15 second period Check connections and retry If current is near typical value 4 0 6 0 A DC nominal and burners will not stay on replace control Clean fla...

Page 28: ...nds after the gas valve GV is energized Simultaneously the electronic air cleaner terminal EAC is energized and remains energized as long as the blower motor BLWM is energized f Heat Off Delay When the thermostat is satisfied the R to W circuit is opened de energizing the gas valve GV stopping gas flow to the burners and de energizing the humidifier terminal HUM 24 VAC The inducer motor IDM will r...

Page 29: ...ector box Condensate trap Condensate trap elbow Gaskets WARNING FIRE EXPLOSION ELECTRICAL SHOCK AND CARBON MONOXIDE POISONING HAZARD Failure to follow this warning could result in dangerous operation personal injury death or property damage Improper installation adjustment alteration service maintenance or use can cause carbon monoxide poisoning explosion fire electrical shock or other conditions ...

Page 30: ...X ECM S Single stage T Two stage FEATURE B Base AFUE Efficiency E Extra AFUE Efficiency C Communicating D Dual Certified 2 pipe or 1 pipe R 2 pipe only S Single stage T Two stage N Standard L Low Nox FEATURE 040 40 000 BTU hr 060 60 000 BTU hr 080 80 000 BTU hr 100 100 000 BTU hr 120 120 000 BTU hr INPUT HEAT 14 14 3 16 17 17 1 2 21 21 24 24 1 2 CABINET WIDTH 10 1000 CFM max 14 1400 CFM max 16 160...

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