System Operation - Maytag Goodman GMS8 Service Instructions Manual

SYSTEM OPERATION

HEATING - Abnormal Operation
The following presents the probable causes of question-
able furnace operation and how to fix them. Look through
the observation window in the blower access door and
make a note of the number of flashes in sequence be-
tween pauses. Next, refer to the Troubleshooting Chart
on the following pages for an interpretation of the LED
signals and to the information in this section for a descrip-
tion of the problem.
1. Internal Control Failure with Integrated Ignition
Control. Check for voltage to the furnace and low volt-
age at the control board. Check for blown fuse on the
control board. If the control determines it has an inter-
nal fault, it enters a locked-out state. Any of the situa-
tions mentioned will cause the diagnostic LED to pro-
vide no signal. The control board should only be re-
placed after all other checks from the Troubleshooting
Chart have been verified.
2. System Lockout. If a flame is not sensed during the
first seven (4) seconds after the gas valve is ener-
gized, the control turns off the gas. There will then be
a 30 second delay while the induced draft blower is
energized to purge the heat exchanger. The ignitor will
next be energized and preheated for (8) seconds. The
gas valve will then be energized. If flame is not sensed
in seven (4) seconds the gas valve will be de-ener-
gized and another purge will occur. The control will
cycle the gas valve a total of three (3) times before it
determines it cannot establish measurable combustion
and enters a locked out state. The diagnostic light code
for this problem is one short flash followed by a longer
pause. The control can be reset and brought out of
lockout mode by turning the thermostat off for more
than (5) seconds and less than (20) seconds and then
back on. It can also be reset by turning off the electri-
cal disconnect switch to the furnace for a minimum of
5 seconds.
NOTE: The control board will automatically reset one hour
after lockout occurs. If the furnace frequently has to be
reset, it means that a problem exists that should be cor-
rected. Refer to Troubleshooting Chart on the following
pages for aid in determining the cause.
3. Pressure Switch Stuck Closed. If the control senses
the pressure switch is closed when the induced draft
blower is off, it waits until the fault is corrected. The
diagnostic light code for this problem is two short
flashes followed by a longer pause. The probable cause
is either a faulty pressure switch or wiring.
4. Pressure Switch Stuck Open. If, after the induced
draft blower is energized, the pressure switch does
not close within 5 minutes, the control will go into a 1-
hour lockout. The control will automatically reset from
lockout adn restart the ignition sequence. The diag-
nostic light code for this problem is three short flashes
followed by a pause. The probable causes are either
disconnected hose to the pressure switch, faulty pres-
sure switch or wiring, or restricted air intake or flue pip-
ing.
5. Open Primary or Auxiliary Limit. If the limit control
opens, the air circulator blower will be turned on until
the limit closes. The induced draft blower will turn off for
5 seconds then turn off. The diagnostic light code for
this problem is four short flashes followed by a pause.
The probable cause is either low conditioned air flow
due to dirty filter or resistance in duct work, faulty limit,
faulty blower, or blower speed set to low.
6. Flame Sensed with No Call for Heat. If the control
senses a flame when the gas valve is de-energized, it
will run the air circulation blower and the induced draft
blower continuously with no further furnace operation.
The diagnostic flash code for this is a five flashes. The
probable causes are either a short to ground in flame
sense circuit, miswiring, lingering burner flame or a slow
closing gas valve.
7. Open Rollout Limit. If the rollout control opens, the air
circulator blower will be energized all the time. The di-
agnostic light code for this problem is six flashes fol-
lowed by a pause. The probable cause is either re-
stricted flue piping or improper air requirements.
8. Low Flame Sense Signal. If the furnace continues to
operate and the micro-amp signal from the flame sen-
sor falls below specified level, the diagnostic light code
for this problem will be seven flashes followed by a
pause. The probable cause is either a coated/oxidized
sensor, incorrectly positioned senser in burner flame
or lazy burner flame due to improper gas pressure or
combustion air.
9. Igniter circuit or poor ground. Improperly connected
igniter, bad igniter or poor ground to the equipment.
The diagnostic light code for this problem is eight
flashes.
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