Operation, Option Switches, Heat Mode | White Rodgers 50M56-743

OPERATION

OPTION SWITCHES

The option switches on the 50M56-743 control are used to determine the length of the heat delay-to-fan-off period, the mode of operation, and the 2nd stage delay period. The following illustration shows the options and the selections of the switch positions. The switches are shown in the factory default positions.

*MODE and 2ND STG DLY for Goodman 50M56-289 only

HEAT MODE

When heat is required, the thermostat will send a call for heat to the control. This starts the control’s heating sequence. The ignitor and humidifier (optional) are powered. The ignitor is powered after the pre-purge period.

Upon initial application of power, the ignitor warm-up time is 17 seconds. The ignitor on-time will then be increased depending on whether or not flame is achieved. The warm-up time is limited to a maximum of 19 seconds. During the first 64 warm- up periods following power-up, the warm-up time may not be less than 17 seconds.

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 19 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.

After the ignitor warm-up period, MV LO (first stage) and MV HI (second stage) are both energized to the gas valve. Flame must be detected within 4 seconds. If flame is detected, the 30-second HEAT delay-to-fan-on period begins. The circulator and electronic air cleaner (optional) will also energize at this time.

1 Stage operation – If the Option Switch MODE (SW1-2) is set to the 1 STG position, both MV LO and MV HI will remain energized.

2 Stage operation – If the Option Switch MODE is set to 2 STG, MV HI will de-energize after 5 seconds, leaving MV LO energized. If the MODE is in the 2 STG position, 2nd STG DLY (SW1-3) will determine the second stage- on delay as follows:

5 MIN – On call for heat, the 5 minute 2nd stage recognition timer begins. After the 5-minute delay, the second stage heat (MV HI) is energized.

AUTO – On call for heat, the automatic second stage will determine the optimum timing between stages for comfort. Auto will adapt the delay to energize MV HI from instantly to up to 12 minutes.

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 25 seconds. When the purge is complete, the inducer blower is 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 50M56-743 control goes into the “retry” sequence. The “retry” sequence provides a 60-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 50M56-743 controller will clear the ignition attempt (or retry) counter. If flame is lost after 10 seconds, it will re-cycle 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

2.0seconds. 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 closing the thermostat contacts. This energizes the 50M56-743 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 satisfied, 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.

MANUAL FAN ON MODE

If the thermostat fan switch is moved to the ON position, the circulator fan (low 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.

50M56-743, 50M56-7433 specifications

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