52
SERVICING
L
INE VOLTAGE NOW PRESENT
WARNING
6. Place unit in heating cycle, measure current draw of ignitor
during preheat cycle.
S-309 CHECKING FOR FLASHBACK
Flashback will also cause burning in the burner venturi, but is
caused by the burning speed being greater than the gas-air
flow velocity coming from a burner port.
Flashback may occur at the moment of ignition, after a burner
heats up or when the burner turns off. The latter is known as
extinction pop.
Since the end results of flashback and delayed ignition can
be the same (burning in the burner venturi) a definite attempt
should be made to determine which has occurred.
If flashback should occur, check for the following:
1. Improper gas pressure - adjust to proper pressure (See
S-307 CHECKING GAS PRESSURE
)..
2. Check burner for proper alignment and/or replace burner.
3. Improper orifice size - check orifice for obstruction.
S-310 CHECKING PRESSURE SWITCH
The pressure control is a safety device to prevent the com
-
bustion cycle from occurring with inadequate venting caused
by a restricted or blocked vent pipe.
WARNING
HIGH
VOLTAGE
D
ISCONNECT
ALL
POWER BEFORE SERVICING OR
INSTALLING THIS UNIT.
M
ULTIPLE POWER SOURCES MAY
BE PRESENT.
F
AILURE TO DO SO MAY CAUSE PROPERTY
DAMAGE, PERSONAL INJURY OR DEATH.
1. Remove burner compartment door to gain access to
pressure switch(es).
2. Remove wires from the pressure switch(es) electrical termi
-
nals.
3. Remove the pressure control hose from the control and
interconnect with an inclined manometer as shown in the
following figures.
With a call for heat and the inducer running, check across the
pressure switch contacts with an ohm meter. If the contacts
are not closed, compare the negative reading on the inclined
manometer with the rating on the pressure switch to determine
whether the switch is defective or if the negative pressure is
inadequate to close the switch.
S-311 HIGH ALTITUDE APPLICATION (USA)
A high altitude kit is required for installations above 7,000 ft.
Refer to the accessory matrix in this manual to determine
the proper natural gas and L.P. gas high altitude kit for your
furnace.
S-312 CHECKING FOR DELAYED IGNITION
Delayed ignition is a delay in lighting a combustible mixture
of gas and air which has accumulated in the combustion
chamber.
Furnace design makes this extremely unlikely unless safety
controls have been by-passed or tampered with. Never by-
pass or alter furnace controls.
If delayed ignition should occur, the following should be
checked:
1. Improper gas pressure - adjust to proper pressure (See
S-307 CHECKING GAS PRESSURE
).
2. Improper burner positioning - burners should be in locating
slots, level front to rear and left to right.
3. Carry over (lighter tube or cross lighter) obstructed - clean.
4. Main burner orifice(s) deformed, or out of alignment to
burner - replace.
S-313 CHECKING INTEGRATED IGNITION
CONTROL BOARDS
NOTE:
Failure to earth ground the furnace, reversing the
neutral and hot wire connection to the line (polarity), or a high
resistance connection in the neutral line may cause the control
to lockout due to failure to sense flame.
T
O AVOID THE RISK OF ELECTRICAL SHOCK, WIRING TO THE UNIT
MUST BE PROPERLY POLARIZED AND GROUNDED.
D
ISCONNECT POWER
BEFORE PERFORMING SERVICE LISTED BELOW.
WARNING
The ground wire must run from the furnace all the way back
to the electrical panel. Proper grounding can be confirmed by
disconnecting the electrical power and measuring resistance
between the neutral (white) connection and the burner closest
to the flame sensor. Resistance should be less than 2 ohms.
The ignition control is a combination electronic and electro
-
mechanical device and is not field repairable. Complete unit
must be replaced.
L
INE VOLTAGE NOW PRESENT
WARNING
These tests must be completed within a given time frame due
to the operation of the ignition control.
The ignition control is capable of diagnosing many furnace
failures to help in troubleshooting. The trial for ignition period
is 4 seconds.
The indicator light/display may be viewed by looking through
the sight glass in the blower compartment door. If the blower
compartment door is removed, failure to hold the door switch
closed while removing the blower compartment door will result
in the loss of the stored failure code. In most cases recycling
the ignition control will result in the same failure code originally
displayed.
