Option Switches, Heat Mode, Operation | White Rodgers 50A55-743

OPTION SWITCHES

The option switches on the 50A55-743 control are used to determine the length of the heat delay-to-fan-off periods. The following table shows the time periods that will result from the various switch positions.

OPTION SWITCH POSITIONS

HEAT delay-	Set switch
to-fan-off:	#1	#2
90 sec.	On	On
120 sec.	Off	On
150 sec.**	On	Off
180 sec.	Off	Off

**Factory setting

HEAT MODE

In a typical system, a call for heat is initiated by closing the thermostat contacts. This starts the 50A55 control’s heating sequence. The inducer blower and optional hu- midifier are energized and the ignitor is powered after the 15 seconds pre-purge period.

This controller has an adaptive algorithm that adjusts the duration of the ignitor warm-up to extend ignitor life.

Upon initial application of power, the warm-up time is 7 seconds. The ignitor on-time will then be increased or decreased depending on whether or not flame is achieved. The warm-up time is limited to a maximum of 9 seconds. During the first 64 warm-up periods following power-up, the warm-up time may not be less than 5 seconds.

Upon a call for heat, if the warm-up time has not been locked, it will be decreased by one second.This reduction of the ignitor on-time will continue until flame fails to be achieved (resulting in a retry).

In the event of a retry, the warm-up time will be increased by one second and locked in at that duration. Once the warm-up time is locked, it remains fixed until another call for heat results in a retry, in which case the warm-up time is again increased by one second and remains locked.

In the event of two successive retry attempts, the warm-up time will be unlocked and set to 9 seconds. If flame is then achieved, the warm-up time will begin adapting again with the next call for heat. If, however, this third attempt fails to achieve flame, the control will go into system lockout.

At the end of the ignitor warm-up time, both valves in the gas valve are opened. Flame must be detected within 4 seconds.

OPERATION

If flame is detected, the delay-to-fan-on period begins.After the delay-to-fan-on period ends, the optional electronic air cleaner is energized and the circulator fan is energized at heat speed.When the thermostat is satisfied, the gas valve is de-energized. After proof of flame loss, the heat delay- to-fan-off period begins and the inducer blower remains energized to purge the system for 15 seconds. When the purge is complete, the inducer blower and humidifier are de-energized. After the delay-to-fan-off period ends, the circulator fan and electronic air cleaner are de-energized.

If flame is not detected, both valves are de-energized, the ignitor is turned off, and the 50A55 control goes into the “retry” sequence. The “retry” sequence provides a 30-second wait following an unsuccessful ignition attempt (flame not detected). After this wait, the ignition sequence is restarted with an additional 1 second of ignitor warm- up time.

If flame is established for more than 10 seconds after ignition, the 50A55 controller will clear the ignition attempt (or retry) counter. If flame is lost after 10 seconds, it will restart the ignition sequence.

During burner operation, a momentary loss of power of 50 milliseconds or longer will de-energize the main gas valve. When power is restored, the gas valve will remain de-energized and a restart of the ignition sequence will begin immediately.

A momentary loss of gas supply, flame blowout, or a shorted or open condition in the flame probe circuit will be sensed within 2.0 seconds.The gas valve will de-energize and the control will restart the ignition sequence.Recycles will begin and the burner will operate normally if the gas supply returns, or the fault condition is corrected.

If the control has gone into system lockout, it may be possible to reset the control by a momentary power interruption of one second or longer. Refer to SYSTEM LOCKOUT FEATURES.

COOL MODE

In a typical system, a call for cool is initiated by clos- ing the thermostat contacts. This energizes the 50A55 control and the compressor. The cool delay-to-fan-on period begins. After the delay period ends, the optional electronic air cleaner is energized, and the circulator fan is energized at cool speed. After the thermostat is satis- fied, the compressor is de-energized and the cool mode delay-to-fan-off period begins. After the delay-to-fan-off period ends, the circulator fan and electronic air cleaner (optional) are de-energized.

50A55-743 specifications

The White Rodgers 50A55-743 is a versatile and highly efficient universal gas furnace control board widely recognized for its reliability and advanced features. Designed to enhance the performance and safety of heating systems, it caters to both residential and commercial applications, making it a preferred choice for HVAC professionals and homeowners alike.

One of the standout features of the 50A55-743 is its universal compatibility. It is designed to work with a variety of gas furnaces from different manufacturers, significantly simplifying the installation and replacement process. This feature saves time and reduces overhead costs for technicians, as they no longer have to stock multiple control boards for various furnace models.

The control board operates using advanced microprocessor technology, which ensures precise control over the heating cycle. This precision translates into optimal comfort for the occupants and can lead to significant energy savings. The board is capable of monitoring and adjusting the heating process in real-time, adapting to the specific demands of the environment.

Another important characteristic of the White Rodgers 50A55-743 is its built-in diagnostics. The board features LED indicators that provide real-time feedback on the furnace's operational status. These diagnostic lights help technicians quickly identify issues, minimizing downtime and improving service efficiency. Together with its user-friendly design, these features make troubleshooting a more straightforward process.

Safety is a paramount consideration in HVAC systems, and the 50A55-743 excels in this aspect as well. It includes multiple safety features such as flame proving, limit control, and lockout capabilities, which enhance the operational integrity of the furnace. These features help to prevent unsafe operating conditions, providing peace of mind for users.

The control board can also work with variable speed blower motors, allowing it to effectively manage airflow and heating output, leading to improved efficiency and comfort levels. Its adaptability to different configurations makes it a powerful component in modern HVAC systems.

In conclusion, the White Rodgers 50A55-743 stands out as a leading control board in the HVAC industry. With its universal compatibility, advanced microprocessor technology, built-in diagnostics, and robust safety features, it represents a significant advancement in furnace control, enhancing reliability, efficiency, and overall user satisfaction. This makes it an excellent choice for anyone looking to upgrade their heating system.