SERVICING
41
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
Single stage furnaces use a 115 volt silicon carbide igniter
(p/n 0130F00008) with 17-second warm up time.
WARNING
Disconnect ALL power before servicing.
1. Remove burner compartment door to gain access to
the ignitor.
2. Ignitor cool - approximately 70 - 77°F.
3. Disconnect the ignitor from the Ignition Control.
4. Using an ohmmeter measure the resistance of the ig-
nitor: at room temperature a normal reading will be
37 - 68 ohms.
5. Reconnect ignitor.
WARNING
Line Voltage now present.
6. Place unit in heating cycle, measure current draw of
ignitor during preheat cycle.
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 burn-
er 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 at
-
tempt 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
CHECKING GAS 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 com-
bustion cycle from occurring with inadequate venting caused
by a restricted or blocked vent pipe.
WARNING
HIGH VOLTAGE
Disconnect ALL power before servicing or in
-
stalling this unit. Multiple power sources may
be present. Failure to do so may cause proper
-
ty 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
terminals.
3. Remove the pressure control hose from the control
and interconnect with a manometer as shown in the
followi
ng figures.
With a call for heat and the inducer running, check across
the pressure switch contacts with an ohm meter. If the con-
tacts are not closed, compare the negative reading on the
manometer with the rating on the pressure switch to deter-
mine whether the switch is defective or if the negative pres-
sure is inadequate to close the switch.
-.
OPEN TO
ATMOSPHERE
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)
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 LP gas high altitude kit for your
furnace.
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
CHECKING GAS PRESSURE
).
