ICP N9MSB Series User Manual

SERVICE AND TECHNICAL SUPPORT MANUAL Gas Furnace: N9MSB
Specifications subject to change without notice.
440 04 4413 03 27
Figure 16 (CONT.)
Troubleshooting Guide − Flow Chart
1 + 2 BLOWER ON AFTER POWER UP –
(115V OR 24V) – Norm
al operation.
Blower runs for 90 seconds, if unit is powered up during a call for heat (R- W/W1 closed) or when (R-W/W1 opens) d
u
ring the blower on-delay period.
6 + 1 IGNITION LOCKOUT – System failed to
ignite gas and prove flame in 4 attemp
ts. Control will auto-reset after 3
hours. Refer to status code #6.
5 ABNORMAL FLAME-PROVING SIGNAL
Flame is proved while gas valve is de- energi
zed. Inducer will run until fault is
cleared. Check for:
- Stuck open or leaky gas valve.
2 PRESSURE SWITCH DID NOT OPEN –
Check for:
- Obstruct
ed pressure tube.
- Pressure switch stuck closed.
3 LPS or HPS PRESSURE SWITCH DID
NOT CLOSE OR REOPENED – If opens
during blower on-delay period, blower will come on for the selected blower off-delay. If LPS open longer than 5 minutes, induc
er
shuts off for 15 minutes before
retry. If HPS open for one minute, then furnace will lockout (after the successive trials) for three hours before retry .
Check for: - Proper vent sizing.
- Air leak between vestibule and blower
compartment.
- Low inlet gas pressure (if LGPS used). - Disconnected or obstructed pressure
tubi
ng.
- Defective or miswired pressure switches - Excessive wind. - P
l
ugged condensate drain
- Water in vent piping, possible sagging pipe -
Restri
cted vent.
- Defective Inducer motor. - Low inducer voltage (115 VAC)
4 LIMIT CIRCUIT FAULT – Indicates the
limit, flame rollout is open. Blower will run for 4 min. or until open switch remakes whichever is longer. If open longer than 3 min, code changes to lockout #7. If open less than 3 min. status code #4 continues to flash until blower shuts off. Flame roll
o
ut switch requires manual reset.
Check for:
- Loose blower wheel.
-
Defective switch or connections.
- Dirty filter or restricted duct system. - Improper gas input adjustment - Improper limit switch or no limit gasket
To determine whether the problem is in the gas valve, igniter, or flame sensor the system can be operated in component test mode. To check the igniter, remove the R thermostat connection from the control, reset power, start the component test.
Do
es 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 betwee
n connector P2 (HSI) and
NEUTRAL-L2 on the control. Was 115V
presen
t for the 15 second period?
Check connections and retry. If current is near typical value (4.0-6.0A DC nominal) and bur
ners will not stay on,
replace control.
Clean flame sensor with fine steel wool and recheck current. Nominal current is 4.0 to 6.0A DC. Is current near typical value?
Replace electrode.
Will main burners ignite and stay on? Replace furnace control. Fixed.
NO
YES
YES YES
NO NO
Replace furnace control. Check for continuity in the harness and igniter. Replace defective component.
Reconnect the R thermostat lead and set thermostat to call for heat. Connect voltmeter across gas valve connections. Does gas valve receive 24V? Does gas valve open and allow gas to flow? Do the main burners ignite? Do the main burners stay on?
Allow blower to come on and repeat test to check for intermittent operation. Check that gas valve electric switch is turned on. Replace valve. Check connections. If OK, replace control. Check for: - Inadequate flame carryover
or rough ignition.
- Low inlet gas pressure. - Proper firing rate.
Repeat call for heat and check flame sensor current during trial for ignition period. Is the DC current below 0.5A?
YES
YES
YES YES
YES NO NO
NO
NO NO NO
6 IGNITION PROVING FAILURE – If flame is
not sensed during the trial for ignition period, the control will repeat the ignition sequence 3 more times before lockout #6 + 1 occurs. If flame signal is lost during the blower on-delay period, blower will come on for the selected blower off-delay. Check th
e fo
llowing before going to the next step.
- Gas valve turned off .
- Man
ual shut-off valve open?
- Green/Yellow wire MUST be connected
to furnace sheet metal.
- Flame sensor must not be grounded.
10 POLARITY – Check for correct line
voltage polarity. If units are twinned, check fo
r proper low-voltage (24V)
transformer phasing.
7 LIMIT CIRCUIT LOCKOUT – Lockout
occurs if the limit, flame rollout is open long
er than 3 minutes. Control will auto-
reset after 3 hours. Refer to status code #4.
8 GAS HEATING LOCKOUT – Control will
NOT auto reset. Turn off power and wait 5 minutes to retry. Check for:
- Stuck closed gas valve relay on control.
-
Miswire or short to gas valve wire.
YES
unless noted on switch.
L12F045

ICP N9MSB Series Specifications

General

Brand	ICP
Model	N9MSB Series
Category	Furnace
Language	English