Two- Stage Multi Position Furnace
Service Manual
39
440 08 2002 02
HONEYWELL SV9541Q “SMART VALVE” Sequence of Operation
POWER APPLIED TO APPLIANCE
THERMOSTAT CALLS FOR HEAT
COMBUSTION BLOWER DE--ENERGIZED
THREE SECOND FLAME
FAILURE RECYCLE DELAY
FIVE MINUTE WAIT PERIOD
PILOT LIGHTS AND FLAME IS SENSED
DURING 90 SECOND TRAIL FOR
IGNITION?
(1)
PILOT VALVE CLOSES;
PILOT IGNITOR OFF
FLAME SENSE LOST?
PILOT AND MAIN VALVE CLOSE
COMBUSTION AIR BLOWER OFF AFTER
POST PURGE
FLAME SENSE LOST MORE THAN FIVE
TIMES IN THIS CALL FOR HEAT?
THERMOSTAT CALL FOR HEAT ENDS
PILOT AND MAIN VALVE CLOSE
CIRCULATING AIR FAN “OFF” AFTER
DELAY
WAIT FOR NEXT CALL FOR HEAT
HI AND LOW AIR PROVING
SWITCHES PROVED OPEN?
NO
NO
NO
NO
YES
YES
WAIT FOR PRESSURE SWITCHES TO OPEN
(1) Ignitor turns “OFF” about 30 seconds into the trial for ignition. If the pilot flame has
not lit, it turns back “ON” for the final 30 seconds of the 90 second trial for ignition.
The pilot valve is energized during the entire trial for ignition. This is normal opera-
tion for the gas ignition system.
(2) If a W2 call for heat is present, circulating fan on high speed. Combustion air blower
and main valve remain on high.
NOTE: If main limit string opens and takes longer than 2 minutes to close, system goes
into 1 hour wait period.
NO
COMBUSTION AIR BLOWER
ON HIGH SPEED
HI AND LOW AIR PROVING SWITCHES
PROVED CLOSED WITHIN 30 SECONDS?
YES
PRE--PURGE
PILOT VALVE OPENS:
IGNITOR POWERED
MAIN VALVE OPENS ON HIGH,
IGNITER “OFF”
CIRCULATINGFAN “ON” AND
COMBUSTION AIR BLOWER ON LOW
SPEED. MAIN VALVE ON LOW FIRE
AFTER DELAY
(2)
CIRCULATING AIR FAN OFF
AFTER DELAY
COMBUSTION BLOWER “OFF” AFTER
POST PURGE