OPERATION

MANUAL FAN ON MODE

If the thermostat fan switch is moved to the ON position, the circulator fan (heat speed) and optional electronic air cleaner are energized. When the fan switch is returned to the AUTO position, the circulator fan and electronic air cleaner (optional) are de-energized.

TWINNING INTERFACE

If the control has six screw terminals, one of which is designated TWIN, the control is equipped with a single wire twinning interface. If twinning is used, either control will process a call for heat, cool or fan as described above. However, after the heat-, cool-, or fan-on delay time ex- pires, both units will energize the circulator blowers at the same time. Likewise, after the heat-, cool-, or fan-off delay time expires, both units will de-energize the circulator blowers at the same time. This allows for proper air flow to be obtained. To assure proper control operation, both controls must share a common transformer ground (TR).

To enable twinning, do the following.

1.Power supplied to both furnaces must be from the same phase of the incoming 120 VAC power.

2.Connect the TWIN screw terminals on the 50A55-743 of the furnaces to be twinned to each other using a single wire (14-22 AWG.).

SYSTEM LOCKOUT AND

DIAGNOSTIC FEATURES

SYSTEM LOCKOUT FEATURES

When system lockout occurs, the gas valve is de-energized, the circulator blower is energized at heat speed, and, if flame is sensed, the inducer blower is energized. The diagnostic indicator light will flash or glow continuously to indicate system status. (System lockout will never override the precautionary features.)

To reset the control after system lockout, do one of the following:

1.Interrupt the call for heat or cool at the thermostat for at least one second but less than 20 seconds (if flame is sensed with the gas valve de-energized, interrupting the call for heat at the thermostat will not reset the control).

2.Interrupt the 24 VAC power at the control for at least one second. You may also need to reset the flame rollout sensor switch.

3.After one hour in lockout, the control will automatically reset itself.

DIAGNOSTIC FEATURES

The 50A55-743 control continuously monitors its own op- eration and the operation of the system. If a failure occurs, the LED will indicate a failure code as shown below. If the failure is internal to the control, the light will stay off. In this case, the entire control should be replaced, as the control is not field-repairable.

If the sensed failure is in the system (external to the control), the LED will flash in the following flash-pause sequences to indicate failure status (each flash will last approximately 0.25 seconds, and each pause will last approximately 2 seconds).

1 flash, then pause

System lockout

2 flashes, then pause

Pressure switch stuck closed

3 flashes, then pause

Pressure switch stuck open

4 flashes, then pause

Open limit switch

5 flashes, then pause

Flame has been sensed when

 

no flame should be present (no

 

call for heat)

6 flashes, then pause

Open rollout switch

7 flashes, then pause

Low flame sense signal

Continuous flashing

115 Volt AC power reversed

OFF

Control failure

ON

Normal operation

The LED will also flash once at power-up.

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White Rodgers 50A55-743 Operation Manual FAN on Mode, Twinning Interface, System Lockout Diagnostic Features
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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.
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