SERVICE AND TECHNICAL SUPPORT MANUAL Gas Furnace: (F/G)9MVE
Specifications subject to change without notice.
29 440 04 4801 03
Figure 17 (CONT.) Troubleshooting Guide − Flow Chart
1 + 2 BLOWER ON AFTER POWER UP –
(115V OR 24V) – Normal 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)
during the blower on-delay period.
6 + 1 IGNITION LOCKOUT – System failed to
ignite gas and prove flame in 4
attempts. 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-
energized. Inducer will run until fault is
cleared. Check for:
- Stuck open or leaky gas valve.
2 PRESSURE SWITCH DID NOT OPEN –
Check for:
- Obstructed pressure tube.
- Pressure switch stuck closed.
3 LOW-HEAT 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 open longer than 5 minutes inducer
shuts off for 15 minutes before retry.
Check for:
- Proper vent sizing.
- Air leak between vestibule and blower
compartment.
- Low inlet gas pressure (if LGPS used).
- Restricted vent.
- Disconnected or obstructed pressure
tubing.
- Defective or miswired pressure switches
- Excessive wind.
- Plugged condensate drain.
- Water in vent piping, possible sagging
pipe.
- Defective Inducer motor.
- Low inducer voltage (115 VAC)
4 LIMIT CIRCUIT FAULT – Indicates the
limit or a flame rollout switch is open or the
furnace is operating in high-heat only
mode due to 2 successive low-heat limit
trips. 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 rollout switch
requires manual reset. Check for:
- Loose blower wheel.
- Defective switch or connections.
- Improper low- or high-heat gas input
adjustment.
- Improper limit switch or no limit gasket.
- Dirty filter or restricted duct system.
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, and put setup switch
SW1-6 in the ON position to start the
component 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 by turning setup
switch SW1-6 OFF and then back ON.
Check for 115V between pin 3 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 nominal) and burners
will not stay on, repeat check
in high-heat. If burners will
still not stay on replace
control. If burners operate in
high-heat then switch to low-
heat, check manifold
pressure. If OK, check
burner carryover and flame
sensor location.
Clean flame sensor with fine steel wool
and recheck current. Nominal current is
4.0 to 6.0 microamps.
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 all gas valves are
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 microamps below 0.5?
YES
YES
YES
YES
YES
NO
NO
NO
NO
NO
NO
YES
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
the following before going to the next step.
- Gas valve turned off.
- Manual shut-off valve.
- GREEN/YELLOW wire MUST be
connected to furnace sheet metal.
- Flame sensor must not be grounded.
2 + 5 INVALID MODEL SELECTION OR SETUP ERROR – If status code 2 + 5
only flashes 4 times on power-up the control is missing its model plug PL4
and is defaulting to the model selection stored in memory. If status code 2 +
5 flashes continuously it could indicate any of the following:
- Model plug PL4 is missing and there is no valid model stored in
permanent memory. This will happen if you forget to install the model
plug PL4 on a service replacement control.
- Thermostat call with SW1-1 ON.
- Thermostat call with SW1-6 ON.
- SW1-1 and SW1-6 both ON.
- Two different furnace models twinned.
- Service replacement control is incorrect. Need non-modulating board with
software version V24 or later.
9 HIGH-HEAT PRESSURE SWITCH OR
RELAY DID NOT CLOSE OR
REOPENED - Check for:
- Control relay may be defective.
- Gas valve is miswired.
- Refer to status code #3.
10 POLARITY – Check for correct line
voltage polarity. If units are twinned,
check for proper low-voltage (24V)
transformer phasing.
7 LIMIT CIRCUIT LOCKOUT – Lockout
occurs if the limit or flame rollout switch is
open longer than 3 minutes or 10
successive limit trips occurred during high-
heat. 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.
NOTE:
NUMBER IN UPPER LEFT HAND
CORNER REPRESENTS FLASH CODE
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