54
SERVICING
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 pres-
sure switch(es).
2. Remove wires from the pressure switch(es) electrical
terminals.
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 nega-
tive pressure is inadequate to close the switch.
OPEN TO
ATMOSPHERE
INCLINED MANOMETER
HOSE TO INDUCED
DRAFT BLOWER TAP
1/4" TEE
INDUCED DRAFT BLOWER
PRESSURE SWITCH
PRESSURE SWITCH
HOSE
INDUCED
DRAFT
BLOWER
*
*
*
*
*
*
*
M
1
2
3
P
C
O
N
O
F
F
COIL COVER
PRESSURE SWITCH
Blower Pressure Switch
Negative Pressure Measurement
S-311 HIGH ALTITUDE APPLICATION (USA)
A high altitude kit is required for installationsabove 7,000 ft.
Refer to the accessory matrix in this manual to determine
the proper natural gas and LP 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 locat-
ing 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 re-
sistance 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 elec-
tromechanical 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 pe-
riod 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.
L
INE VOLTAGE NOW PRESENT
WARNING
These tests must be completed within a given time frame
due to the operation of the ignition control.
1. Check for 120 volts from Line 1 (Hot) to Line 2 (Neutral)
at the ignition control. No voltage, check the door switch
connections and wire harness for continuity.
2. Check for 24 volts from W to C terminal on the ignition
control. No voltage. Check transformer, room thermo-
