32
SERVICING
Gas
Rate
Range
Nominal
High Stage 3.2 to 3.8" w.c. 3.5" w.c.
Low Stage 1.6 to 2.2" w.c. 1.9" w.c.
Manifold Gas Pressure
Natural Gas
WARNING
HIGH
VOLTAGE
D
ISCONNECT
ALL
ELECTRICAL POWER AND SHUT OFF GAS SUPPLY
BEFORE SERVICING OR INSTALLING.
Gas
Rate
Range
Nominal
High Stage 9.7 to 10.3" w.c. 10.0" w.c.
Low Stage 5.7 to 6.3" w.c. 6.0" w.c.
Manifold Gas Pressure
Propane Gas
CHECKING HOT SURFACE IGNITOR
120V Silicon Nitride Igniter -
*M/CEC96
use a 120V silicon
nitride igniter for ignition. The normal op
erating temperature
is approximately 2156°F - 2678°F.
At room temperature the
igniter ohm reading should be from 37-68 ohms.
7. Place unit in heating cycle, measure current draw of
ignitor during preheat cycle.
The steady state current at 120V is 0.37 to 0.68 amps.
8. After checking and/or replacing of hot surface ignitor,
reinstall burner compartment door and verify proper unit
operation.
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.
2. Check burner for proper alignment and/or replace
burner.
3. Improper orifice size - check orifice for obstruction.
CHECKING PRESSURE SWITCH
The pressure control is a safety device to prevent the
combustion cycle from occurring with inadequate venting
caused by a restricted or blocked vent pipe.
1. Remove burner compartment door to gain access to
pressure 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.
4. With an ohm meter connected across the pressure
switch terminals; with the inducer running the switch
should close and the ohm meter should show a com
-
plete circuit across the pressure switch. If the switch
is not closed, compare the negative pressure to the
closing point specified for the particular switch. Either
the switch is defective or the inducer / venting system
is inadequate.
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
ON
O
F
F
COIL COVER
PRESSURE SWITCH
Blower Pressure Switch
Negative Pressure Measurement
HIGH ALTITUDE APPLICATION (USA)
The furnace as shipped requires no change to run between
0 - 7500 feet. Do not attempt to increase the firing rate by
changing orifices or increasing the manifold pressure be
-
low 7500 feet. feet. This can cause poor combustion and
equipment failure. High altitude installations above 7500
feet. 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 7500 feet. 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.
