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6
OPERATION
OPTION SWITCHES
The option switches on the 50M56U-843 control are used
to determine the length of the heat delay-to-fan-off period,
themodeofoperation,and the2ndstagedelayperiod.The
following illustration shows the options and the selections of
the switch positions. The switches are shown in the factory
default positions.
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.
Uponinitialapplicationofpower,theignitorwarm-uptimeis17
seconds. The ignitor on-time will then be increased depending
on whether or not flame is achieved. The warm-up time is
limitedtoamaximumof19seconds.Duringtherst64warm-
up periods following power-up, the warm-up time may not be
lessthan17seconds.
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
timeislocked,itremainsxeduntilanothercallforheatresults
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
timewillbeunlockedandsetto19seconds.Ifameisthen
achieved, the warm-up time will begin adapting again with the
nextcallforheat.If,however,thisthirdattemptfailstoachieve
flame, the control will go into system lockout.
Aftertheignitorwarm-upperiod,MVLO(rststage)andMV
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–IftheOptionSwitchMODE(SW1-2)is
settothe1STGposition,bothMVLOandMVHIwillremain
energized.
2 Stage operation (Goodman 50M56-289 Application only)
–IftheOptionSwitchMODEissetto2STG,MVHIwillde-
energize after 5 seconds, leaving MV LO energized. If the
MODEis inthe 2STG position,2nd STGDLY(SW1-3) will
determine the second stage- on delay as follows:
5 MIN–Oncallforheat,the5minute2ndstagerecognition
timer begins. After the 5-minute delay, the second stage heat
(MVHI)isenergized.
AUTO –Oncall forheat, theautomatic secondstage will
determine the optimum timing between stages for comfort.
AutowilladaptthedelaytoenergizeMVHIfrominstantlyto
upto12minutes.
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
for25seconds.Whenthepurgeiscomplete,theinducerblower
is de-energized. After the delay-to-fan-off period ends, the
circulator fan and electronic air cleaner are de-energized.
*
*
*MODE and 2ND STG DLY for Goodman 50M56-289 only
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”sequenceprovidesa60-second
wait following an unsuccessful ignition attempt (flame not
detected). After this wait, the ignition sequence is restarted
withanadditional1secondofignitorwarm-uptime.
Ifameisestablishedformorethan10secondsafterignition,
the 50M56U-843 controller will clear the ignition attempt (or
retry)counter.Ifameislostafter10seconds,itwillre-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 gasvalve willde-energizeand thecontrol
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 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.
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.
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
precautionaryfeatures.)
To reset the control after system lockout, do one of the
following:
1. Interruptthecallforheatorcoolatthethermostatforat
least one secondbut less than20 seconds (if ame is
sensed with the gas valve de-energized, interrupting the
call for heat at the thermostat will not reset the control).
2. Interruptthe24VACpoweratthecontrolforatleastone
second. You may also need to reset the ame rollout
sensor switch.
3. After one hour in lockout, the control will automatically
reset itself.