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SERVICING
S-308 CHECKING HOT SURFACE IGNITOR
120V Mini Igniter Single Stage -
furnaces use a 120V car
-
bide mini igniter for ignition. (part# 20165703) or a
Silicon Nitride igniter (part# 0130F00008) The normal
operating temperature is approximately 2550°F - 2876°F.
D
ISCONNECT
ALL
POWER BEFORE SERVICING.
WARNING
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 ignitor:
Mini Igniter : Carbide Mini Igniter should read between
30 to 300 ohms.
5. Reconnect ignitor.
120V Silicon Nitride Igniter
- furnaces with a 120V sil
-
icone nitride igniter; The normal operating temperature
is approximately 2156°F-2678°F. At room temperature
the igniter ohm reading should be from 37-68 ohms.
L
INE VOLTAGE NOW PRESENT
WARNING
6. After checking and/or replacing of hot surface ignitor,
reinstall burner compartment door and verify proper unit
operation.
S-309 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 (See
S-307 CHECKING GAS PRESSURE
)..
2. Check burner for proper alignment and/or replace burner.
3. Improper orifice size - check orifice for obstruction.
S-310 CHECKING PRESSURE SWITCH
The pressure switch a safety device to prevent the combus-
tion cycle from occurring with inadequate venting caused by a
restricted or blocked vent pipe on the 80% and 90% furnaces.
1. Remove burner compartment door to gain access to
pressure switch(es).
2. Remove wires from the pressure switch(es) electrical
terminals.
3. Using a VOM check from common terminal to NC (Nor
-
mally Closed) - should read open.
If switch reads as above proceed to Step 4, otherwise re-
place control.
4. Remove the pressure control hose from the control and
interconnect with an inclined manometer as shown in the
following figures.
ID Blower Pressure Switch
Negative Pressure Measurement
(80% Upflow Single-Stage Furnace Shown,
Counterflow Similar)
