27
SERVICING
WARNING
HIGH VOLTAGE
Disconnect 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
S-308 CHECKING HOT SURFACE IGNITOR
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.
WARNING
Disconnect ALL Gas and Electric Power Supply.
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.
WARNING
Line Voltage now present.
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.
120V Silicone Nitride Igniter
- (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.
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 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 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.
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.
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 figures.
