Specifications
7
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 SELECT BUTTON for approximately
two seconds or until the diagnostic LED turns off. Release the
button 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 SELECT BUTTON for five to ten seconds or until
the diagnostic LED begins to rapid flash. When the button 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 flash will stop and the LED will
be on to indicate return to normal status.
The 50M56U-751 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-751
control. There are no other user serviceable parts.
OPERATION
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 50M56U-751 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 in Troubleshooting
section. The control will store the last five fault codes. 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,asthecontrolisnoteld-repairable.
Failure codes will flash the LED 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).
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