System Operation - Goodman AMH8 Service Instructions Manual

SYSTEM OPERATION

HEATING - Abnormal Operation
The following presents the probable causes of questionable
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 between 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 description of the problem.
1. Internal Control Failure with Integrated Ignition Con-
trol. Check for voltage to the furnace . Check for blown
fuse on the control board. If the control determines it
has an internal fault, it enters a locked-out state. Any of
the situations mentioned will cause the diagnostic LED
to provide no signal. The control board should only be
replaced after all other checks from the Troubleshoot-
ing Chart have been verified.
2. System Lockout. If a flame is not sensed during the
first seven (4) seconds after the gas valve is energized,
the control turns off the gas. There will then be a 30
second delay while the induced draft blower is ener-
gized to purge the heat exchanger. The ignitor will next
be energized and preheated for (17) seconds. The gas
valve will then be energized. If flame is not sensed in
seven (4) seconds the gas valve will be de-energized
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 electrical discon-
nect 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 diagnostic light
code for this problem is three short flashes followed
by a pause. The probable causes are either discon-
nected hose to the pressure switch, faulty pressure switch
or wiring, or restricted air intake or flue piping.
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
diagnostic light code for this problem is six flashes
followed by a pause. The probable cause is either re-
stricted flue piping or improper air requirements. An
open fuse will also cause this fault code.
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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