SYSTEM OPERATION
28
HEATING - Abnormal Operation
The following presents the probable causes of questionable
furnace operation and how to fix them. Look through the ob
-
servation 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
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 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
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 energized, 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. 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 lock
-
out 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 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 corrected. 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 2
flashes
. 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 and restart
the ignition sequence. The diagnostic light code for this
problem is
three short flashes
followed by a pause. The
probable causes are either disconnected hose to the pres-
sure 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 contin
-
uously 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, miswir
-
ing, lingering burner flame or a slow closing gas valve.
7.
Open Rollout Limit / Open control board fuse.
If the roll
-
out 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 restricted flue piping or improper air requirements.
If fuse is open, check for short in thermostat circuit.
8.
Low Flame Sense Signal.
If the furnace continues to
operate and the micro-amp signal from the flame sensor
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 sensor 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
.
