27
SERVICING
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.
120V Mini Igniter Single Stage - furnaces use a 120V car-
bide mini igniter for ignition. The normal operating tempera-
ture is approximately 2550°F - 2876°F. At room temperature
a good igniter will have an ohm reading range of 50 - 300.
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.
6. Place unit in heating cycle, measure current draw of
ignitor during preheat cycle.
Models using 120V Mini Igniter:
Should read approximately 1 amp maximum. The
steady state current at 120V is a nominal of .7 plus or
minus .3 amps.
7. After checking and/or replacing of hot surface ignitor,
reinstall burner compartment door and verify proper
unit operation. - (pt #
0130F00008) furnaces with a 120V silicone nitride
igniter; The normal operating temperature is approx-
imately 2156° F - 2678° F. At room temperature the
igniter ohm reading should be from 37-68 ohms.
Flashback will also cause burning in the burner venturi, but
is caused by the burning speed being greater than the gas-
air ow 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 o. The latter is known
as extinction pop.
Since the end results of ashback and delayed ignition can
be the same (burning in the burner venturi) a denite attempt
should be made to determine which has occurred.
If ashback 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 orice size - check orice for obstruction.
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
(Normally 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 gures.
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