Lennox International Inc. G24-200 - Manual (Page 40)

Page 40
Troubleshooting
HEATING SEQUENCE OF OPERATION WITH TWO-STAGE THERMOSTAT
NORMAL HEATING MODE ABNORMAL HEATING MODE
YES
YES
POWER ON
IS THE S47 (S69) ROLLOUT SWITCH CLOSED?
B6 (B15) COMBUSTION AIR BLOWER
PREPURGE FOR 30 SECS.
DETERMINE WHY AUTOMATIC-RESET
S10 (S99) HIGH LIMIT OPEN.
YES
NO
NO
8 SEC TRIAL FOR IGNITION − START IGNITION
TRAIL, GV1 (GV3) GAS VALVE OPENS ON LOW
HEAT. IS FLAME SENSED WITHIN 8 SECS?
CONTINUED NEXT PAGE
THERMOSTAT CALLS FOR HEAT
(W1 ENERGIZED)
K13 RELAY ENERIZED.
A3 (A12) IGNITION CONTROL LED ON.
IS THE S10 (S99) HIGH LIMIT CLOSED?
CHECK VENTING SYSTEM
OPERATION/BLOCKAGE BEFORE
RESETTING THE MANUALLY-RESET S47
(S69) ROLLOUT SWITCH.
IS THE B6 (B15) COMBUSTION
AIR BLOWER ON?
CHECK K13−1 CONTACT OPERATION AND
WIRING TO B6 (B15) COMBUSTION AIR
BLOWER?
NO
YES
IS THE S18 (S45) COMBUSTION AIR
BLOWER PROVING SWITCH CLOSED?
CHECK SENSING TUBE FOR BLOCKAGE
AND S18 (S45) SWITCH FOR PROPER
OPERATION.
NO
NO
GV1 (GV3) GAS VALVE CLOSED, SPARK
OFF. INCREMENT TRAIL REGISTER.
(DURING RETRY PERIOD LED FLASHES
.5 SEC. ON AND 2.5 SEC. OFF. ARE THE
THREE TRIALS COMPLETE?
LOCKOUT OCCURS. TO RESET A3 (A12)
IGNITION CONTROL MOVE THERMOSTAT
SWITCH FROM HEAT TO OFF TO HEAT.
K56 (K57) RELAY ENERGIZED. K25 CIRCUIT
BOARD ENERGIZED. SYSTEM BLOWERS ON
AFTER 45 SEC DELAY.
YES
CHECK BELT.
CHECK RELAYS.
YES
NO
YES
NOTE − THIS FURNACE FUNCTIONS WITH TWO INDEDPENDENTLY CONTROLLED HEAT SECTIONS.
THE GRAY BOXES INDICATE COMPONENTS WHICH EFFECT BOTH HEAT SECTIONS SIMULTANEOUSLY.
NO
YES
NO
FLAME SENSE OK?