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HEATING SEQUENCE OF OPERATION WITH TWO-STAGE THERMOSTAT CONTINUED
NORMAL HEATING MODE
ABNORMAL HEATING MODE
YES
HAS ROOM AIR TEMPERATURE CONTINUED
TO DROP BELOW THE THERMOSTAT"S
W2 SET POINT?
DETERMINE WHY AUTOMATIC-RESET
S10 (S99) HIGH LIMIT OPEN. K20, (K123), K36
RELAYS MAINTAIN BLOWER OPERATION.
IS THE S10 (S99) HIGH LIMIT CLOSED?
IS W1 DEMAND SATISFIED?
A3 (A12) LED OFF
YES
B6 (B15) COMBUSTION
AIR BLOWER OFF.
B3 SYSTEM BLOWERS OFF
AFTER 150 SEC DELAY.
NO
YES
NO
POWER FROM W2
ENERGIZES K19 RELAY
SECOND-STAGE OF GV1 (GV3)
GAS VALVE ENERGIZED (HIGH HEAT)
AFTER APPROXIMATELY 3 SEC.
IS W2 DEMAND SATISFIED?
YES
CLOSE SECOND-STAGE OF
GV1 (GV3) GAS VALVE AFTER
APPROXIMATELY 3 SEC. AND THEN
RETURN TO LOW HEAT OPERATION.
LED CODES
1 − ON NORMAL OPERATION WITH THERMOSTAT CALLING FOR HEAT.
2 − 0.5 SEC ON AND 2.5 SECS OFF IN IGNITION RETRY PERIOD.
3 − OFF NO POWER OR DETECTED FAULT.
FIRST-STAGE OF GV1 (GV3)
GAS VALVE CLOSES.
NOTE − IF ECONOMIZER INSTALLED, ECONOMIZER OPERATES WHEN BLOWER POWERED.