SERVICING
59
If switch reads as above proceed to Step 4, otherwise
replace control.
4. Remove the pressure control hose from the control
and interconnect with an inclined manometer as shown
in the following figure.
Modulating
Gas Valve
Front Cover
Pressure
Switch
Low & High
Pressure Switch
Assembly
Modulating Furnace Pneumatic Tubing Diagram
Upflow Model Shown
For representation only. Actual unit may vary in appearance.
S-311 HIGH ALTITUDE APPLICATION
Modulating furnaces are approved up to 10,000 ft al-
titude. No kit or changes are needed.
S-312 CHECKING FOR DELAYED IGNITION
Delayed ignition is a delay in lighting a combustible mix-
ture of gas and air which has accumulated in the combus-
tion chamber.
When the mixture does ignite, it may explode and/or
rollout causing burning in the burner venturi.
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 CON-
TROL 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 con-
firmed by disconnecting the electrical power and measur-
ing resistance between the neutral (white) connection and
the burner closest to the flame sensor. Resistance should
be less than 10 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 controls utilize a
dual, 7-segment LED display to indicate diagnostic codes.
When the control is powered up normally the light will be
on continuously. The contol display will indicate
"ON"
when
powered and in standby mode.
This can be used to test for 120 volts and 24 volts to the
control since both must be present for the light to be on. If
this step fails, check for 120 volts to the control and check
the transformer and its associated wiring. If this step is
successful give the control a call for heat and wait five (5)
seconds or until the furnace goes into lockout. If the con-
trol detects a failure it will now be shown on the diagnostic
indicator light/display. Refer to the
Abnormal Operation
section in the
Sequence of Operation
section of this manual
for more detail on failure codes
The indicator light/display may be viewed by looking
through the sight glass in the blower compartment door.
The failure codes are retrieved via an on-board, momen-
tary push button switch. Pressing the button for 2-5 sec-
onds will force the failure codes to be displayed on the
diagnostic indicator.
