Lennox ML193UHE Series Unit Information page 51

Heating Sequence of Operation Continued
N O R M A
15 SECOND COMBUSTION AIR INDUCER PREPURGE
INITIATED BY CLOSED PRESSURE SWITCH.
IGNITOR WARM UP -- 20 SECONDS.
4 SECOND TRIAL FOR IGNITION.
GAS VALVE OPENS. IGNITOR ENERGIZED FOR
FIRST 3 SECONDS OF THE TRIAL.
FLAME STABILIZATION PERIOD.
4 SECONDS
FLAME RECTIFICATION CURRENT
CHECK. CAN FLAME BE PROVEN WITHIN
4 SECONDS AFTER GAS VALVE OPENS?
FLAME PRESENT?
FLAME SIGNAL 1.5 MICROAMPS OR GREATER?
INDOOR BLOWER ON
AFTER 30-SECOND DELAY
PRIMARY LIMIT SWITCH CLOSED?
ROLLOUT SWITCH CLOSED?
COMBUSTION AIR PRESSURE
SWITCH CLOSED?
THERMOSTAT DEMAND SATISFIED.
LED SLOW FLASH.
COMB. AIR INDUCER CONTINUES 5 SECOND
POST PURGE AFTER T'STAT DEMAND IS SATISFIED.
INDOOR AIR BLOWER COMPLETES SELECTED "OFF"
DELAY BEFORE SHUTTING OFF.
HEATING SEQUENCE CONTINUED
L H E A T N I G M O D E
YES
YES
YES
(0.5 microamps)
YES
YES
YES
YES
YES
YES
YES
YES
YES
A B N O R M A
NO
IS VOLTAGE ABOVE 70 VOLTS?
YES
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
INDOOR BLOWER OFF.
HAS CONTROL FAILED TO SENSE FLAME FOR
NO
FIVE CONSECUTIVE TRIES DURING A SINGLE
HEAT DEMAND?
LED SIGNAL WATCHGUARD FAILURE CODE
WATCHGUARD MODE. GAS VALVE OFF.
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF WITH DELAY
IS 60 MINUTE RESET PERIOD COMPLETE?
NO
HAS CONTROL RESET IGNITION
SEQUENCE FOUR TIMES?
NO
LED FLASHES CODE 4 - LOW FLAME
SIGNAL.
(Does not affect operation of control)
LED FLASHES CODE 7 - PRIMARY LIMIT OPEN
GAS VALVE DE-ENERGIZED.
COMBUSTION AIR INDUCER DE-ENERGIZED.
NO
INDOOR BLOWER ON UNTIL SWITCH CLOSES.
LIMIT SWITCH CLOSED?
YES
HAS PRIMARY LIMIT RESET
TIME EXCEEDED 3 MINUTES?
NO
LED FLASHES CODE 8 - ROLLOT SWITCH OPEN.
GAS VALVE POWER OFF. COMBUSTION AIR INDUCER POWER
ON. INDOOR BLOWER ON SEQUENCE HOLDS UNTIL ROLLOUT
SWITCH IS RESET AND MAIN POWER IS INTERRUPTED OR
THERMOSTAT IS CYCLED OFF/ON FOR 1 SEC. MINIMUM.
NO
HAS PRESSURE SWITCH OPENED 5 TIMES
IN THE SAME HEAT DEMAND?
NO
GAS VALVE DE-ENERGIZED. COMBUSTION AIR
INDUCER ON. INDOOR BLOWER OFF WITH
DELAY. HAS CAB PRESSURE SWITCH CLOSED
WITHIN 2.5 MINUTES?
NO
5 MINUTE PRESSURE SWITCH
WATCHGUARD MODE.
Page 51
L H E A T N I G M O D E
LED FLASHES CODE 13 -
LOW LINE VOLTAGE.
NO
ONCE VOLTAGE IS ABOVE
75 VOLTS, HEATING
SEQUENCE RESTARTS.
YES
LED FLASHES CODE
7 - PRIMARY LIMIT
OPEN. GAS VALVE,
COMB. AIR INDUCER
NAL LIMIT SWITCH
OPEN UNTIL MAIN
POWER IS
INTERRUPTED OR
T'STAT IS CYCLED
OFF/ON FOR 1 SEC.
MINIMUM. 60-MINUTE
RIOD STARTS AT
YES
TIME LIMIT CLOSES.
IS 60-MIN. PERIOD
COMPLETE?
NO
LED FLASHES
CODE 10
1 HR PRESSURE
YES
SWITCH
WATCHGUARD
YES
NO
YES
NO
YES
MODE