If ﬂame is not detected, both valves are de-energized, the
ignitor is turned off, and the 50M56U-843 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.
The option switches on the 50M56U-843 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
If ﬂame is established for more than 10 seconds after ignition,
the 50M56U-843 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.
*MODE and 2ND STG DLY for Goodman 50M56-289 only
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.
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.
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.
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.
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 a typical system, a call for cool is initiated by closing the
thermostat contacts. This energizes the 50M56U-843 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.
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
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.
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
SYSTEM LOCKOUT AND
2 Stage operation (Goodman 50M56-289 Application only)
– 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.
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
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.
To reset the control after system lockout, do one of the
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
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.
3. After one hour in lockout, the control will automatically