Lennox ML193UHE Series User Manual

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Troubleshooting: Heating Sequence of Operation (Continued)
HEATING SEQUENCE CONTINUED
NORMAL HEATING MODE ABNORMAL HEATING MODE
FLAME RECTIFICATION CURRENT
CHECK. CAN FLAME BE PROVEN WITHIN
4 SECONDS AFTER GAS VALVE OPENS?
(0.5 microamps)
FLAME PRESENT?
INDOOR BLOWER ON
AFTER 30-SECOND DELAY
PRIMARY LIMIT SWITCH CLOSED?
COMBUSTION AIR PRESSURE
SWITCH CLOSED?
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.
INDOOR BLOWER ON UNTIL SWITCH CLOSES.
LIMIT SWITCH CLOSED?
GAS VALVE DE-ENERGIZED.
COMBUSTION AIR INDUCER ON.
INDOOR BLOWER OFF WITH DELAY
HAS CAI SWITCH CLOSED IN 2.5 MINUTES?
15‐SECOND COMBUSTION AIR INDUCER PREPURGE
INITIATED BY CLOSED PRESSURE SWITCH.
YES
IGNITOR WARM‐UP -- 20 SECONDS.
YES
YES
FLAME STABILIZATION PERIOD.
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
INDOOR BLOWER OFF.
HAS CONTROL FAILED TO SENSE FLAME FOR
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?
YES
4 SECONDS
YES
HAS CONTROL RESET IGNITION
SEQUENCE FOUR TIMES?
FLAME SIGNAL 1.5 MICROAMPS OR GREATER?
YES
YES
YES
ROLLOUT SWITCH CLOSED?
LED FLASHES CODE 8 - ROLLOUT 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.
YES
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.
YES
NO
5‐MINUTE PRESSURE SWITCH
WATCHGUARD MODE.
YES
IS VOLTAGE ABOVE 70 VOLTS?
LED FLASHES CODE 13 -
LOW LINE VOLTAGE.
ONCE VOLTAGE IS ABOVE
75 VOLTS, HEATING
SEQUENCE RESTARTS.
NO
YES
YES
YES
NO
NO
NO
NO
NO
NO
YES
YES
NO
NO
NO
YES
YES
HAS PRIMARY LIMIT RESET
TIME EXCEEDED 3 MINUTES?
LED FLASHES CODE
7 - PRIMARY LIMIT
OPEN. GAS VALVE,
COMB. AIR INDUCER
AND INDOOR BLOW
ER OFF. LEDs SIGNAL
LIMIT SWITCH OPEN
UNTIL MAIN
POWER IS
INTERRUPTED OR
T'STAT IS CYCLED
OFF/ON FOR 1 SEC.
MINIMUM. 60-MINUTE
WATCHGUARD PE
RIOD STARTS AT
TIME LIMIT CLOSES.
IS 60-MIN. PERIOD
COMPLETE?
NO
YES
4‐SECOND TRIAL FOR IGNITION.
GAS VALVE OPENS. IGNITOR ENERGIZED FOR
FIRST 3 SECONDS OF THE TRIAL.
LED FLASHES
CODE 10
1 HR PRESSURE
SWITCH
WATCHGUARD
MODE
HAS PRESSURE SWITCH OPENED 5
TIMES IN SAME HEAT DEMAND
NO
YES

Lennox ML193UHE Series Specifications

General

Brand	Lennox
Model	ML193UHE Series
Category	Furnace
Language	English