Troubleshooting: Heating Sequence of Operation (Continued)

HEATING SEQUENCE CONTINUED

NORMAL HEATING MODE

ABNORMAL HEATING MODE

15-SECOND COMBUSTION AIR INDUCER PREPURGE

INITIATED BY CLOSED PRESSURE SWITCH.

YES

IGNITOR WARM-UP −− 20 SECONDS.

YES

4-SECOND TRIAL FOR IGNITION.

GAS VALVE OPENS. IGNITOR ENERGIZED FOR

FIRST 3 SECONDS OF THE TRIAL.

 

 

 

 

 

 

LEDS SIGNAL

NO

 

NO

ALTERNATING

 

 

 

IS VOLTAGE ABOVE 90 VOLTS?

FAST FLASH UNTIL

 

 

 

 

 

 

 

 

 

 

VOLTAGE IS ABOVE

 

 

 

YES

 

 

95 VOLTS, THEN

 

 

 

 

 

 

RESTARTS HEATING

 

 

 

 

 

 

SEQUENCE.

 

 

 

 

 

 

 

YES

FLAME STABILIZATION PERIOD.

4 SECONDS

FLAME RECTIFICATION CURRENT

CHECK. CAN FLAME BE PROVEN WITHIN 4 SECONDS AFTER GAS VALVE OPENS?

(0.5 microamps)

YES

FLAME PRESENT?

NO

NO

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?

WATCHGUARD MODE. GAS VALVE OFF.

COMBUSTION AIR INDUCER OFF.

INDOOR BLOWER OFF WITH DELAY

LEDs SIGNAL WATCHGUARD FAILURE CODE.

IS 60-MINUTE RESET PERIOD COMPLETE?

HAS CONTROL RESET IGNITION

SEQUENCE FOUR TIMES?

NO

YES

YES

NO

YES

FLAME SIGNAL 1.5 MICROAMPS OR GREATER?

YES

INDOOR BLOWER ON

AFTER 30−SECOND DELAY

YES

PRIMARY AND SECONDARY LIMIT

SWITCHES CLOSED?

YES

ROLLOUT SWITCH CLOSED?

YES

COMBUSTION AIR PRESSURE

SWITCH CLOSED?

 

 

 

 

YES

NO

LOW FLAME SIGNAL

LIMIT SWITCH WATCHGUARD

(Does not affect operation of control)

MODE. GAS VALVE, COMB. AIR

 

 

 

 

LED #1 −− SLOW FLASH

INDUCER AND INDOOR BLOW-

 

 

LED #2 −− FAST FLASH

ER OFF. LEDs SIGNAL LIMIT

 

 

 

SWITCH OPEN UNTIL MAIN

 

 

 

 

POWER IS

 

 

GAS VALVE DE−ENERGIZED.

 

INTERRUPTED OR

 

 

 

T’STAT IS CYCLED

 

 

COMBUSTION AIR INDUCER DE−ENERGIZED.

 

 

OFF/ON FOR 1 SEC.

NO

INDOOR BLOWER ON UNTIL SWITCH CLOSES.

MINIMUM. 60−MINUTE

 

 

LED #1 −− SLOW FLASH. LED #2 −− ON.

 

 

WATCHGUARD PE-

 

 

IS LIMIT SWITCH CLOSED?

 

 

 

 

RIOD STARTS AT

 

 

YES

 

 

 

 

TIME LIMIT CLOSES.

 

 

 

 

 

 

HAS PRIMARY / SECONDARY

YES

IS 60−MIN. PERIOD

 

 

 

COMPLETE?

 

 

LIMIT RESET TIME

 

 

 

 

 

 

 

EXCEEDED 3 MINUTES?

 

 

 

 

 

 

NO

NO

GAS VALVE POWER OFF.

 

 

 

COMBUSTION AIR INDUCER POWER ON.

 

 

 

INDOOR BLOWER ON

 

 

 

 

 

 

LED #1 −− ON. LED #2 −− SLOW FLASH.

 

 

 

SEQUENCE HOLDS UNTIL ROLLOUT SWITCH IS RESET

NO

AND MAIN POWER IS INTERRUPTED OR

THERMOSTAT IS CYCLED OFF/ON FOR 1 SEC. MINIMUM.

 

 

 

 

 

 

 

YES

THERMOSTAT DEMAND SATISFIED.

YES

LED #1 & #2 SIMULTANEOUS SLOW FLASHES.

YES

COMB. AIR INDUCER CONTINUES 5-SECOND

POST PURGE AFTER T’STAT DEMAND IS SATISFIED. INDOOR AIR BLOWER COMPLETES SELECTED

DELAY BEFORE SHUTTING OFF.

HAS PRESSURE SWITCH OPENED 5

TIMES IN THE SAME HEAT DEMAND?

NO

YES

GAS VALVE DE−ENERGIZED.

COMBUSTION AIR INDUCER ON.

INDOOR BLOWER OFF WITH DELAY LED #1 −− OFF. LED #2 −− SLOW FLASH. HAS CAB SWITCH CLOSED IN 2.5 MINUTES?

NO

5-MINUTE PRESSURE SWITCH

WATCHGUARD MODE.

1HR

PRESSURE

SWITCH

WATCHGUARD

MODE

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Lennox International Inc Merit Series Gas Furnace installation instructions Heating Sequence

Merit Series Gas Furnace specifications

Lennox International Inc. is a leading name in the heating and cooling industry, and their Merit Series Gas Furnace embodies the commitment to quality and efficiency that the company is known for. The Merit Series is designed to provide reliable heating in a sustainable manner, making it an excellent choice for homeowners seeking comfort without excessive energy bills.

One of the standout features of the Merit Series Gas Furnace is its efficiency ratings. The units in this series typically boast Annual Fuel Utilization Efficiency (AFUE) ratings of up to 95%. This level of efficiency means that the furnace converts a significant portion of the fuel it uses into heat, ultimately lowering operating costs. Such energy-efficient performance is not only beneficial for the wallet but also promotes environmental sustainability.

The Merit Series also incorporates advanced technologies that enhance its operation. The inclusion of a multi-speed blower motor is a notable feature that provides thoughtful airflow management throughout the home. By adjusting the speed according to the heating needs, the furnace optimizes comfort levels while minimizing noise and energy consumption. Homeowners can enjoy a warm environment without the disruptive sounds often associated with traditional furnaces.

Moreover, the Merit Series comes equipped with durable construction materials designed to withstand the test of time. From the robust heat exchanger to the heavy-gauge cabinet, Lennox focuses on longevity and reliability. This ensures that homeowners can trust their furnace to operate effectively even in the harshest winter conditions.

Safety features are also integral to the design of the Merit Series Gas Furnace. With an integrated Flame Sensor and a built-in safety shut-off system, the furnace ensures that any irregularities in operation are promptly detected and addressed. Such measures provide peace of mind for families using the heating system throughout the cold months.

Installation and maintenance are further simplified with the Merit Series. Its design facilitates easier access for HVAC professionals, allowing for quicker installations and routine service, ensuring that homeowners spend less time and money on upkeep.

In conclusion, Lennox International Inc.'s Merit Series Gas Furnace combines efficiency, advanced technology, and robust construction, making it a top choice for families looking to enhance their home's heating system. With its energy-saving innovations and commitment to reliability, the Merit Series stands as an exemplary option in today’s market.