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On every call for heat, the S89 performs a safe start check. If
a flame or a flame simulating condition is present, the S89
locks out without starting the igniter and must be reset.
Following the safe start check and, on the S89F, a valve on
delay period, the S89 spark generator contacts close to
energize the spark generator and the igniter. At the same time
the gas control, powered through the gas valve relay contacts
in the S89, opens so gas can flow to the burner. The igniter is
on during approximately the first 80 percent of the ignition, or
lockout timing, period. During the balance of the lockout timing
period, the ignition is off and the flame sensor attempts to
prove the flame. The flame is proved when current from the
flame sensor through the burner flame to ground reaches
0.8 µA dc.
VALVE-ON DELAY
(S89F ONLY)
TRIAL FOR
OPERATION
TROUBLESHOOTING
WARNING
Fire or Explosion Hazard.
Can cause severe injury, death, or property
damage.
START
THERMOSTAT
1
CALLS FOR HEAT.
SAFE
START
SAFE START
CHECK
2
CHECK
VALVE-ON DELAY
2A
(S89F ONLY)
COMBUSTION
AIR BLOWER
STARTS.
SPARK GENERATOR
IGNITION
3
POWERED. IGNITION
BEGINS AND GAS
CONTROL OPENS.
BURNER LIGHTS.
4
IGNITION STOPS
AND FLAME
CURRENT IS
SENSED.
BURNER
BURNER RUNS
5
S89 MONITORS
FLAME CURRENT.
THERMOSTAT
6
SATISFIED. GAS
CONTROL CLOSES,
BURNER GOES OFF.
END
Fig. 4. Normal sequence of operation.
S89E,F DIRECT SPARK IGNITION CONTROL MODULE
If flame is proved, the gas control remains open and the
burner on until the call for heat ends.
If flame is not proved, the gas control closes and the system is
locked out until the S89 is reset.
If flame is lost after being proved, the S89 will close the gas
control, perform a safe start check, and, on the S89F, valve on
delay, then return ignition as described above.
The S89 is reset by turning the thermostat below room
temperature or removing power to the system for 45 seconds.
POWER INTERRUPTION.
SYSTEM SHUTS OFF. RESTARTS
WHEN POWER IS RESTORED.
IF FLAME SIMULATION
CONDITION IS PRESENT,
SYSTEM WILL NOT START.
IF NO SPARK, S89 LOCKS OUT
AND SHUTS DOWN SYSTEM.
MUST BE RESET.
IF FLAME CURRENT IS ABSENT,
WEAK, OR UNSTEADY, S89
LOCKS OUT AND SHUTS DOWN
SYSTEM. MUST BE RESET.
IF FLAME IS LOST, S89 CLOSES
GAS CONTROL, THEN RESTARTS
SAFE START CHECK AND TRIAL
FOR IGNITION.
Any replacement S89 must have the same or shorter
lockout timing and the same or longer delay timing as
the original control.
7
M19838A
68-0066—4
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