50A55-743
Integrated Furnace Control
INSTALLATION INSTRUCTIONS
FAILURETO READ AND FOLLOW ALL INSTRUCTIONS CAREFULLY BEFORE
INSTALLING OR OPERATING THIS CONTROL COULD CAUSE PERSONAL
INJURY AND/OR PROPERTY DAMAGE.
DESCRIPTION
The 50A55-743 is an automatic gas interrupted ignition
control that employs a microprocessor to continually
monitor, analyze, and control the proper operation of the
gas burner, inducer, and fan.
Signals interpreted during continual surveillance of the
thermostat and flame sensing element initiate automatic
ignition of the burner, sensing of the flame, and system
shut-off during normal operation.
These controls incorporate system fault analysis for quick
gasflowshut-off,coupledwithautomaticignitionretryupon
sensing a fault correction.It is designed as a replacement
for the following controls:
Goodman
White-Rodgers
0130F00005
PCBBF110
PCBBF123
50A55-743
50A55-289
50T55-289
0130F00005S PCBBF110S PCBBF123S
B1809926
PCBBF112
B1809926S
PCBBF112S
PRECAUTIONS
WARNING
Installation should be done by a qualified heating and air
conditioning contractor or licensed electrician.
!
Failure to comply with the following warnings could
If in doubt about whether your wiring is millivolt, line, or
low voltage, have it inspected by a qualified heating and
air conditioning contractor or licensed electrician.
result in personal injury or property damage.
FIRE HAZARD
• Do not exceed the specified voltage.
• Replace existing control with exact model and
dash number.
• Protectthecontrolfromdirectcontactwithwater
(dripping, spraying, rain, etc.).
• If the control has been in direct contact with
water, replace the control.
• Label all wires before disconnection when
servicing controls. Wiring errors can cause
improper and dangerous operation.
Do not exceed the specification ratings.
All wiring must conform to local and national electrical
codes and ordinances.
This control is a precision instrument, and should be
handled carefully. Rough handling or distorting compo-
nents could cause the control to malfunction.
Followinginstallationorreplacement,followmanufacturer’s
recommended installation/service instructions to ensure
proper operation.
• Route and secure wiring away from flame.
SHOCK HAZARD
• Disconnect electric power before servicing.
• Ensure proper earth grounding of appliance.
CAUTION
!
• Ensure proper connection of line neutral and
Donotshortoutterminalsongasvalveorprimary
control. Short or incorrect wiring may damage
the thermostat.
line hot wires.
EXPLOSION HAZARD
• Shut off main gas to appliance until installation
is complete.
PART NO. 37-7348A
1226
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WIRING
TYPICAL SYSTEM WIRING DIAGRAM
HOT
(LINE)
NEUTRAL
(LINE)
120 VAC
24 VAC CLASS II
TRANSFORMER
TH
24 VAC
50A55
TR
COOL
HEAT
PARK
PARK
LINE
XFMR
EAC
HUM
IND-N
IND
CIRCULATOR
BLOWER
INDUCER
IGNITOR
IGN
IGN-N
HUMIDIFIER
CIR N
LINE N
XFMR N
HUM N
EAC N
ELECTRONIC
AIR CLEANER
Y
W
G
R
Y
W
G
R
COMPRESSOR
CONTACTOR
50A55
in other
furnace(s)
—
THERMOSTAT
TWINNING
C
APPLICATIONS
ONLY
TWIN*
TWIN*
PRESSURE SWITCH (N. O.)
PS
PSO
HLI
HLO
FP
RO1
GND
RO2
MV
FLAME
SENSOR
PROBE
HIGH LIMIT
(N. C.)
AUX. HIGH
LIMIT (N. C.)
ROLLOUT
(N. C.)
GAS
VALVE
MV
TR
TH
LEGEND
* The twinning feature is available only on models with
six screw terminals; one of these terminals will be
designated “TWIN”. All 50A55 controls used in
twinning applications must have the “TWIN” terminal.
Low Voltage (24 VAC)
Line Voltage (120 VAC)
N. C. = Normally closed switch
N. O. = Normally open switch
3
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WIRING
TYPICAL SYSTEM WIRING TABLE
50A55
TERMINAL
TERMINAL
SYSTEM COMPONENT
CONNECTION
TYPE
W
G
R
Y
low voltage thermostat W terminal (or equivalent)
low voltage thermostat G terminal (or equivalent)
low voltage thermostat R terminal (or equivalent)
low voltage thermostat Y terminal (or equivalent)
(2nd wire from Y terminal goes to 24 VAC HOT side of
compressor contactor coil)
Terminal
block with
captive
screws
C
24 VAC COMMON side of compressor contactor coil
one wire twinning terminal
TWIN*
MV (2 terminals)
gas valve (both gas solenoids are connected in parallel)
24 VAC transformer (low voltage COMMON side)
24 VAC transformer (low voltage HIGH side)
rollout switch OUTPUT
TR
TH
RO1
RO2
FP
12-pin
rollout switch INPUT
flame sensor probe†
connector
& harness
PS
pressure switch INPUT
PSO
HLI
pressure switch OUTPUT
high limit INPUT
HLO
GND
high limit OUTPUT
MUST BE RELIABLY GROUNDED TO CHASSIS
2-pin
connector
& harness
IND
IGN
inducer HOT side
ignitor HOT side
spade terminal
spade terminal
spade terminal
spade terminal
spade terminal
spade terminal
spade terminal
spade terminal
spade terminal
spade terminal
spade terminal
spade terminal
spade terminal
spade terminal
COOL
circulator blower COOL SPEED terminal
circulator blower HEAT SPEED terminal
unused circulator blower terminals
input voltage (120 VAC) HOT side
24 VAC transformer line voltage HOT side
electronic air cleaner HOT side
humidifier HOT side
HEAT
PARK (2 terminals)
LINE
XFMR
EAC (optional)
HUM (optional)
CIR N
circulator blower NEUTRAL terminal
input voltage (120 VAC) NEUTRAL side
24 VAC transformer line voltage NEUTRAL side
electronic air cleaner NEUTRAL side
humidifier NEUTRAL side
LINE N
XFMR N
EAC N (optional)
HUM N (optional)
IND-N
inducer NEUTRAL side
IGN-N
ignitor NEUTRAL side
* The twinning feature is available only on models with six screw terminals; one of these terminals
will be designated “TWIN”. All 50A55 controls used in twinning applications must have the “TWIN”
terminal.
† Maximum recommended flame probe wire length is 36 inches.
4
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OPERATION
Ifflameisdetected,thedelay-to-fan-onperiodbegins.After
thedelay-to-fan-onperiodends,theoptionalelectronicair
cleaner is energized and the circulator fan is energized at
heatspeed.Whenthethermostatissatisfied,thegasvalve
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 15 seconds.When the
purge is complete, the inducer blower and humidifier are
de-energized. After the delay-to-fan-off period ends, the
circulator fan and electronic air cleaner are de-energized.
OPTION SWITCHES
The option switches on the 50A55-743 control are used to
determine the length of the heat delay-to-fan-off periods.
The following table shows the time periods that will result
from the various switch positions.
OPTION SWITCH POSITIONS
HEAT delay-
to-fan-off:
Set switch
#1
#2
90 sec.
120 sec.
150 sec.**
180 sec.
On
Off
On
Off
On
On
Off
Off
If flame is not detected, both valves are de-energized,
the ignitor is turned off, and the 50A55 control goes into
the “retry” sequence. The “retry” sequence provides a
30-secondwaitfollowinganunsuccessfulignitionattempt
(flame not detected).After this wait, the ignition sequence
is restarted with an additional 1 second of ignitor warm-
up time.
**Factory setting
HEAT MODE
If flame is established for more than 10 seconds after
ignition, the50A55controllerwillcleartheignitionattempt
(or retry) counter. If flame is lost after 10 seconds, it will
restart the ignition sequence.
In a typical system, a call for heat is initiated by closing
the thermostat contacts. This starts the 50A55 control’s
heating sequence. The inducer blower and optional hu-
midifier are energized and the ignitor is powered after the
15 seconds pre-purge period.
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
This controller has an adaptive algorithm that adjusts
the duration of the ignitor warm-up to extend ignitor life.
Upon initial application of power, the warm-up time is 7 begin immediately.
seconds. The ignitor on-time will then be increased or
A momentary loss of gas supply, flame blowout, or a
decreaseddependingonwhetherornotflameisachieved.
The warm-up time is limited to a maximum of 9 seconds.
During the first 64 warm-up periods following power-up,
the warm-up time may not be less than 5 seconds.
shorted or open condition in the flame probe circuit will be
sensedwithin2.0seconds.Thegasvalvewillde-energize
andthecontrolwillrestarttheignitionsequence.Recycles
will begin and the burner will operate normally if the gas
Upon a call for heat, if the warm-up time has not been supply returns, or the fault condition is corrected.
locked, it will be decreased by one second.This reduction
If the control has gone into system lockout, it may be
of the ignitor on-time will continue until flame fails to be
possible to reset the control by a momentary power
achieved (resulting in a retry).
interruption of one second or longer. Refer to SYSTEM
In the event of a retry, the warm-up time will be increased LOCKOUT FEATURES.
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
COOL MODE
In a typical system, a call for cool is initiated by clos-
ing the thermostat contacts. This energizes the 50A55
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 satis-
fied, 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.
is again increased by one second and remains locked.
Intheeventoftwosuccessiveretryattempts,thewarm-up
time will be unlocked and set to 9 seconds.If flame is then
achieved, thewarm-uptimewillbeginadaptingagainwith
the next call for heat. If, however, this third attempt fails
to achieve flame, the control will go into system lockout.
At the end of the ignitor warm-up time, both valves in the
gas valve are opened. Flame must be detected within 4
seconds.
5
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OPERATION
MANUAL FAN ON MODE
If the thermostat fan switch is moved to the ON position,
the circulator fan (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.
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
issensedwiththegasvalvede-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.
TWINNING INTERFACE
If the control has six screw terminals, one of which is
designated TWIN, the control is equipped with a single
wire twinning interface. If twinning is used, either control
will process a call for heat, cool or fan as described above.
However, after the heat-, cool-, or fan-on delay time ex-
pires, both units will energize the circulator blowers at the
same time.Likewise, after the heat-, cool-, or fan-off delay
time expires, both units will de-energize the circulator
blowers at the same time. This allows for proper air flow
to be obtained. To assure proper control operation, both
controls must share a common transformer ground (TR).
3. Afteronehourinlockout, thecontrolwillautomatically
reset itself.
DIAGNOSTIC FEATURES
The 50A55-743 control continuously monitors its own op-
eration and the operation of the system.If a failure occurs,
the LED will indicate a failure code as shown below.If the
failure is internal to the control, the light will stay off.
In this case, the entire control should be replaced, as
the control is not field-repairable.
To enable twinning, do the following.
1. Power supplied to both furnaces must be from the If the sensed failure is in the system (external to the
same phase of the incoming 120 VAC power.
control), the LED will flash 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).
2. ConnecttheTWINscrewterminalsonthe50A55-743
of the furnaces to be twinned to each other using a
single wire (14-22 AWG.).
1 flash, then pause
System lockout
2 flashes, then pause Pressure switch stuck closed
3 flashes, then pause Pressure switch stuck open
4 flashes, then pause Open limit switch
SYSTEM LOCKOUT AND
DIAGNOSTIC FEATURES
5 flashes, then pause Flame has been sensed when
no flame should be present (no
call for heat)
SYSTEM LOCKOUT FEATURES
Whensystemlockoutoccurs,thegasvalveisde-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.)
6 flashes, then pause Open rollout switch
7 flashes, then pause Low flame sense signal
Continuous flashing
115 Volt AC power reversed
Control failure
OFF
ON
Normal operation
The LED will also flash once at power-up.
6
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NOTES
7
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White-Rodgers is a business
of Emerson Electric Co.
The Emerson logo is a
trademark and service mark
of Emerson Electric Co.
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