SERVICING
53
S-311 HIGH ALTITUDE APPLICATION (USA)
Check your furnace rating plate to determine its rated altitude
(either 4500 or 5500 ft). Do not attempt to increase the firing
rate by changing orifices or increasing the manifold pressure
below 4500/5500 feet. This can causepoor combustion
and equipment failure. High altitude installations above
4500/5500 feet may require both a pressure switch and an
orifice change. These changes are necessary to compensate
for the natural reduction in the density of both the gasfuel
and the combustion air at higher altitude.
For installations above 4500/5500 feet, please refer to your
distributor for required kit(s). Contact the distributor for a
tabular listing of appropriate manufacturer’s kits for propane
gas and/or high altitude installations. The indicated kits must
be used to insure safe and proper furnace operation. All
conversions must be performed by a qualified installer, or
service agency.
In some areas the gas supplier may artificially derate the
gas in an effort to compensate for the effects of altitude. If
the gas is artificially derated the appropriate orfice size must
be determined based on the BTU/ft
3
content of the derated
gas and the altitude. Refer to the National Fuel Gas Code,
NFPA 54/ANSI Z223.1, and information provided by the gas
supplier to determine the proper orifice size.
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 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 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 10 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.
NOTE:
The models use
White-Rodgers 50X57- 289
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 thermostat,
and wiring.
If you have 24 volts coming off the transformer but receive
approximately 13 volts on the terminal board between (C)
and (R), check for blown fuse.
3. Check for 120 volts to the induced draft blower by mea-
suring voltage between Pin 1 (on the 2-pin connector) and
Line (Neutral) on the control board. No voltage, replace
ignition control.
4. If voltage is present in Steps 1 through 3 and the induced
draft blower is operating, check for 120 volts to the ignitor
during the preheat cycle. Measure voltage between Pin 2
(on the 2-pin connector) and Line (Neutral) on the control
board. No voltage, check pressure switch.
5. After the ignitor warmup time, begin checking for 24
volts to the gas valve. Voltage will be present for seven
seconds only if proof of flame has been established.
