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7
OPERATION
DIAGNOSTIC FEATURES
The 50M56U-843 control continuously monitors its own
operation and the operation of the system. If a failure occurs,
the LEDwill indicatea failure codeas shownon page8. If
thefailureisinternaltothecontrol,theLEDwillstayoff
orash8times.Inthiscase,theentirecontrolshouldbe
replaced,asthecontrolisnoteld-repairable.
Failure codes will ash the LED in the following ash-
pause sequences to indicate failure status (each flash will
last approximately 0.25 seconds, and each pause will last
approximately2seconds).
FAULT RECALL
The last five fault codes stored can be displayed on the
diagnostic LED. When the control is in standby mode (no
call for heat or cool), press the FAULT RECALL switch for
approximatelytwosecondsoruntilthediagnosticLEDturns
off. Release the switch and the LED will remain off for two
seconds. Then the fault codes will display beginning with the
most recent fault first with a two second pause between codes.
After thestored fault codeshave alldisplayed, theLED will
remain off for two seconds and then turn on to indicate return
to normal status. While displaying the stored fault codes, the
control will ignore any new call for heat, cool or fan.
FAULT CODE RESET
The stored fault codes can be erased from memory. When
the control is in standby mode (no call for heat or cool), press
the FAULT RECALL switch for five to ten seconds or until
thediagnosticLEDbeginstorapidash.Whentheswitchis
released,theLEDwillturnofffortwosecondstoindicatethe
codesareerased.AftertwosecondstheLEDwillturnonto
indicate return to normal status. If the switch is held pressed
forovertensecondstherapidashwillstopandtheLEDwill
be on to indicate return to normal status.
The50M56U-843hasonlyoneserviceablepart–anautomotive
type fuse, which protects the low voltage transformer from
damage if the output is short-circuited. If the fuse has opened
up, remove whatever caused the short circuit and replace
the fuse with only a 3 Amp automotive type fuse. If the fuse
does not correct the condition, replace the entire 50M56U-843
control. There are no other user serviceable parts.
Auto Restart – After one (1) hour of internal or external
lockout, the control will automatically reset itself and go
into an auto restart purge for 60 seconds.
Cool Delay-To-Fan-Off –The period of time between the
loss of a call for cool and the deactivation of the blower
motor at Cool speed.
Cool Delay-To-Fan-On – The period of time after a thermostat
demand for cool before energizing the circulator blower
motor at Cool speed.
Flame Failure Response Time (FFRT) – The period of time
between loss of the supervised main burner flame and
the action to shut off the gas supply.
Heat Delay-To-Fan-Off –The period of time between the
loss of a call for heat and the deactivation of the blower
motor at Heat speed.
Heat Delay-To-Fan-On –Theperiodoftimebetweenproof
of the supervised main burner flame and the activation of
the blower motor at Heat speed.
Igniter Warm-up Time – The length of time allowed for the
igniter to heat up prior to the initiation of gas flow.
Ignition Activation Period (IAP) – The period of time
between energizing the main gas valve and deactivation
of the ignition means prior to the end of TFI.
Inter-purge –The period oftime intendedto allowforthe
dissipation of any unburned gas or residual products of
combustion between the failed trial for ignition and the
retry period.
Post-purge Time –Theperiodoftimeintendedtoallowfor
the dissipation of any unburned gas or residual products
of combustion at the end of a furnace burner operating
cycle. Post-purge begins at the loss of flame sense.
Pre-purge Time –Theperiodoftimeintendedtoallowforthe
dissipation of any unburned gas or residual products of
combustion at the beginning of a furnace operating cycle
prior to initiating ignition.
Recycles – The additional attempts within the same
thermostat cycle for ignition after loss of the supervised
ignition source or the supervised main burner flame.
Retries–Theadditionalattemptswithinthesamethermostat
cycle for ignition when the supervised main burner flame
is not proven within the first trial for ignition period.
TrialforIgnitionPeriod(TFI) – The period of time between
initiation of gas flow and the action to shut off the gas flow
in the event of failure to establish proof of the supervised
ignition source or the supervised main burner flame.
DEFINITION OF TERMS