Service Guide
SYSTEM OPERATION
7
The following presents the probable causes of questionable
furnace operation and how to x them. Look through the
observation window in the blower access door and make a
note of the number of ashes 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.
Check for voltage to the furnace and low voltage
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 The
control board should only be replaced after all other
checks from the Troubleshooting Chart have been veried.
2. If a ame is not sensed during the rst
seven (4) seconds after the gas valve is energized, the
control turns o 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 ame 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
followed by a longer pause. The control can be reset
and brought out of lockout mode by turning the thermostat
o for more than (5) seconds and less than (20) seconds
and then back on. It can also be reset by turning o the
electrical disconnect switch to the furnace for a minimum
of 5 seconds.
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. If the control senses the
pressure switch is closed when the induced draft blower
is o, it waits until the fault is corrected. The diagnostic
light code for this problem is followed
by a longer pause. The probable cause is either a faulty
pressure switch or wiring.
4. 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 followed by a pause.
The probable causes are either disconnected hose to
the pressure switch, faulty pressure switch or wiring, or
restricted air intake or ue piping.
5. If the limit control opens, the air
circulator blower will be turned on until the limit closes. The
induced draft blower will turn o for 5 seconds then turn
o. The diagnostic light code for this problem is
followed by a pause. The probable cause is either
low conditioned air ow due to dirty lter or resistance in
duct work, faulty limit, faulty blower, or blower speed set
to low.
6. If the control
senses a ame 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 ash code for this is a . The
probable causes are either a short to ground in ame
sense circuit, miswiring, lingering burner ame or a slow
closing gas valve.
7. If the rollout control opens, the
air circulator blower will be energized all the time. The
diagnostic light code for this problem is
followed by a pause. The probable cause is either
restricted ue piping or improper air requirements.
8. If the furnace continues to
operate and the micro-amp signal from the ame sensor
falls below specied level, the diagnostic light code for
this problem will be followed by a pause.
The probable cause is either a coated/oxidized sensor,
incorrectly positioned senser in burner ame or lazy burner
ame due to improper gas pressure or combustion air.
9. Improperly connected
igniter, bad igniter or poor ground to the equipment. The
diagnostic light code for this problem is .