White Rodgers 50A55-843 User manual

FIRE HAZARD
• Do not exceed the specified voltage.
• Protect the control from direct contact with water
(dripping, spraying, rain, etc.).
• Ifthecontrolhasbeenindirectcontactwithwater,
replace the control.
• Label all wires before disconnection when servic-
ing controls. Wiring errors can cause improper
and dangerous operation.
• Route and secure wiring away from flame.
SHOCK HAZARD
• Disconnect electric power before servicing .
• Ensure proper earth grounding of appliance.
• Ensure proper connection of line neutral and line
hot wires.
EXPLOSION HAZARD
• Shut off main gas to appliance until installation is
complete.
Printed in U.S.A.
50A55-843
Universal Integrated Furnace Control
FAILURETOREADANDFOLLOWALLINSTRUCTIONSCAREFULLYBEFORE
INSTALLING OR OPERATING THIS CONTROL COULD CAUSE PERSONAL
INJURY AND/OR PROPERTY DAMAGE.
DESCRIPTION
Operator: Save these instructions for future use!
INSTALLATION INSTRUCTIONS
WHITE-RODGERS
EMERSON ELECTRIC CO.
9797 REAVIS ROAD
ST. LOUIS, MISSOURI 63123-5398
www.white-rodgers.com
The 50A55-843 is an automatic gas interrupted ignition control
that employs a microprocessor to continually monitor, analyze,
andcontrolthe proper operationofthegasburner,inducer, and
fan.
Signals interpreted during continual surveillance of the thermo-
stat and flame sensing element initiate automatic ignition of the
burner,sensingoftheflame, and systemshut-offduringnormal
operation.
PRECAUTIONS
PART NO. 37-6265F
Replaces 37-6265E
0327
Installation should be done by a qualified heating and air
conditioning contractor or licensed electrician.
If in doubt about whether your wiring is millivolt, line, or low
voltage, have it inspected by a qualified heating and air condi-
tioning contractor or licensed electrician.
Do not exceed the specification ratings.
Allwiringmustconformtolocalandnationalelectricalcodesand
ordinances.
This control is a precision instrument, and should be handled
carefully.Roughhandlingordistortingcomponentscouldcause
the control to malfunction.
Following installation or replacement, follow manufacturer’s
recommendedinstallation/serviceinstructionsto ensureproper
operation.
CONTENTS
Description......................................................... 1
Precautions........................................................ 1
Specifications..................................................... 2
Installation.......................................................... 3
Mounting & Wiring
Operation ........................................................... 6
Mounting Hole Template.....................................8
These controls incorporate system fault analysis for quick gas
flowshut-off,coupledwith automaticignitionretryuponsensing
a fault correction.
WARNING
Failure to comply with the following
warnings could result in personal injury
or property damage.
CAUTION
Do not short out terminals on gas valve or primary
control. Short or incorrect wiring may damage the
thermostat.

2
SPECIFICATIONS
ELECTRICAL RATINGS [@ 77°F (25°C)]:
Input Voltage: 25 VAC 50/60 Hz
Max. Input Current @ 25 VAC: 0.45 amp
Relay Load Ratings:
Valve Relay: 1.5 amp @ 25 VAC 50/60 Hz 0.6 pf
Ignitor Relay: 6.0 amp @ 120 VAC 50/60 Hz
(resistive)
Inducer Relay: 2.2 FLA–3.5 LRA @ 120 VAC
Circulator Relay: 14.5 FLA–25.0 LRA @ 120 VAC
Flame Current Requirements:
Minimum current to insure flame detection: 1 µa DC*
Maximum current for non-detection: 0.1 µa DC*
Maximum allowable leakage resistance: 100 M ohms
*Measured with a DC microammeter in the flame probe lead
OPERATING TEMPERATURE RANGE:
-40°to 175°F (-40°to 80°C)
HUMIDITY RANGE:
5% to 93% relative humidity (non-condensing)
MOUNTING:
Surface mount multipoise
Timing Specs: (@ 60 Hz**) maximum
Flame Establishing Time: 0.8 sec
Flame Failure Response Time: 2.0 sec
** At 50 Hz, all timing specifications should be increased by
20%
Gases Approved: Natural, Manufactured, Mixed, Liquified
Petroleum, and LP Gas Air Mixtures are all approved for use.
TIMING SPECIFICATIONS
(All times are in seconds, unless noted otherwise)
PRE-PURGE
INITIAL IGNITOR WARM-UP
(1st 64 attempts)
MINIMUM IGNITOR WARM-
UP
MAXIMUM IGNITOR WARM-
UP
IGNITION ACTIVATION
PERIOD
TRIAL FOR IGNITION
PERIOD
RETRIES
VALVE SEQUENCE PERIOD
INTERPURGE
POST-PURGE
LOCKOUT TIME
HEAT DELAY-TO-FAN-ON*
HEAT DELAY-TO-FAN-OFF*
COOL DELAY-TO-FAN-ON
COOL DELAY-TO-FAN-OFF*
AUTO RESET
HUMIDIFIER
ELECTRONIC AIR CLEANER
30
17
5
21
1
4
2 times
12
60
15
300
30, 45
60/90/
120/180
5
45, 90
60 minutes
YES
YES
50A55-843
* These times will vary depending on
option switch position. The control is
factory-set at 30 seconds heat delay-
to-fan-on, 180 seconds heat delay-to-
fan-off and 45 seconds cool delay-to-
fan-off. See OPERATION section for
further information.

3
INSTALLATION
MOUNTING AND WIRING
All wiring should be installed according to local and national
electrical codes and ordinances.
The control must be secured to an area that will experience a
minimum of vibration and remain below the maximum ambient
temperature rating of 175°F. The control is approved for mini-
mum ambient temperatures of -40°F.
When mounting the control, any orientation is acceptable.
Choosea location thatwillnot damage,obstructor place stress
on the control’s terminations, system wiring harness or system
components. After finding a suitable location, drill four (4) 1⁄8”
holes for mounting control. To ensure proper mounting hole
locations, there is a mounting hole template on page 8 of this
instruction sheet. Detach the page with the template from the
instruction sheet and apply it to the mounting location. When
drilling the holes, take care so that the transformer, wiring
harnessorothersystemcomponentsarenotdamaged.Four(4)
#8sheetmetalscrewsareprovidedtocompletetheinstallation.
Refer to the wiring diagram and wiring table when connecting
the 50A55 control to other components of the system.
ULapproved,105°Crated18gauge,stranded, 2⁄64”thickinsula-
tion wire is recommended for all low voltage safety circuit
connections. Refer to 50A55 specification sheet for recom-
mended terminals to mate with those on the control.
UL approved 105°C rated 16 gauge min., stranded, 4⁄64” thick
insulationwireis recommended foralllinevoltage connections.
Refer to 50A55 specification sheet for recommended terminals
to mate with those on the control.
Afterinstallationorreplacement,followappliancemanufacturer’s
recommended installation or service instructions to ensure
proper operation.
The 50A55 has only one serviceable part–an automotive type
fuse, which protects the low voltage transformer from damage
ifits outputisshort-circuited. Ifthefuse hasopenedup, remove
whatevercausedthe short circuitandreplacethefuse with only
a 3 Amp automotive type fuse. If the fuse is not the cause of the
control’s problem, replace the entire 50A55 control. There are
no other user serviceable parts.
Additional jumper wires are included in this package and
should be used if the original wiring does not reach the control
after mounting. Refer to the furnace wiring diagram for proper
connection of the wires.
An additional wiring harness (WR 115-0223) is included in this
package. If the control being replaced has a 2-pin (inducer/
ignitor) connector, this wiring harness will adapt the furnace
wiring to the 4-pin connector of the replacement control.
Trane application - Jumper wire 151-2906 (provided with
control)must beinstalledon thefurnace from R01to R02 ofthe
12-pin connector.
WARNING
CAUTION
FIRE HAZARD
• Do not exceed the specified voltage.
• Replace existing control with exact model and
dash number.
• Protect the control from direct contact with water
(dripping, spraying, rain, etc.).
• Label all wires before disconnection when servic-
ing controls. Wiring errors can cause improper
and dangerous operation.
• Route and secure wiring away from flame.
SHOCK HAZARD
• Disconnect electric power before servicing .
• Ensure proper earth grounding of appliance.
• Ensure proper connection of line neutral and line
hot wires.
EXPLOSION HAZARD
• Shut off main gas to appliance until installation is
complete.
Do not short out terminals on gas valve or primary
control. Short or incorrect wiring may damage the
thermostat.

4
TH
TR
MV
MV
GND
FP
HLO
HLI
PS
C
R
G
W
Y
EAC N
HUM N
XFMR N
LINE N
CIR N
IGN
IND
IGN N
IND N
HUM
EAC
XFMR
LINE
PARK
PARK
HEAT
COOL
IGNITOR
Y
W
G
R
THERMOSTAT
GAS
VALVE
HIGH LIMIT
(N. C.)
ROLLOUT
(N. C.)
AUX. HIGH
LIMIT (N. C.)
PRESSURE SWITCH (N. O.)
FLAME
SENSOR
PROBE
COMPRESSOR
CONTACTOR
ELECTRONIC
AIR CLEANER
HUMIDIFIER
INDUCER
CIRCULATOR
BLOWER
50A55
24 VAC
120 VAC
24 VAC CLASS II
TRANSFORMER
HOT
(LINE) NEUTRAL (LINE)
TH TR
Low Voltage (24 VAC)
Line Voltage (120 VAC)
LEGEND
N. C. = Normally closed switch
N. O. = Normally open switch
RO1
RO2
TYPICAL SYSTEM WIRING DIAGRAM
TWIN*TWIN*
50A55-843
in other
furnace(s)
—
TWINNING
APPLICATIONS
ONLY

5
50A55
TERMINAL TERMINAL TYPE SYSTEM COMPONENT CONNECTION
TYPICAL SYSTEM WIRING TABLE
W
G
R
Y
C
TWIN*
MV (2 terminals)
TR
TH
RO1
RO2
FP
PS
HLI
HLO
GND
(unused terminal)
IND
IGN
IND N
IGN N
COOL
HEAT
PARK (2 terminals)
LINE
XFMR
EAC (optional)
HUM (optional)
CIR N
LINE N
XFMR N
EAC N (optional)
HUM N (optional)
Terminal
block with
captive
screws
12-pin
connector
& harness
4-pin
connector
& harness
spade terminal
spade terminal
spade terminal
spade terminal
spade terminal
spade terminal
spade terminal
spade terminal
spade terminal
spade terminal
spade terminal
spade terminal
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)
24 VAC COMMON side of compressor contactor coil
one wire twinning terminal
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
rollout switch INPUT
flame sensor probe*
pressure switch INPUT
high limit INPUT
high limit OUTPUT
MUST BE RELIABLY GROUNDED TO CHASSIS
inducer HOT side
ignitor HOT side
inducer NEUTRAL side
ignitor NEUTRAL side
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
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
* The twinning feature is available only on models with six screw terminals; one of these terminals
will be designated “TWIN”. All 50A55-843 controls used in twinning applications must have the
“TWIN” terminal.
†
Maximum recommended flame probe wire length is 36 inches.

6
OPERATION
OPTION SWITCHES
The option switches on the 50A55-843 control are used to
determine the length of the cool delay-to-fan-off, heat delay-to-
fan-on and heat delay-to-fan-off periods. The following table
shows the time periods that will result from the various switch
positions.
HEAT MODE
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 humidifier are
energized and the ignitor is powered within one second.
This controller has an adaptive algorithm that adjusts the dura-
tion of the ignitor warm-up, to extend ignitor life. Upon initial
application of power, the warm-up time is 17 seconds. The
ignitor on-time will then be increased or decreased depending
onwhetherornotflameisachieved.Thewarm-uptimeislimited
to a maximum of 21 seconds. During the first 64 warm-up
periods following power-up, the warm-up time may not be less
than 17 seconds.
Upon a call for heat, if the warm-up time has not been locked, it
willbedecreasedbyonesecond.Thisreductionoftheignitoron-
time will continue until flame fails to be achieved (resulting in a
retry).
Intheeventofaretry,thewarm-uptimewillbeincreasedbytwo
seconds 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 whichcase thewarm-up timeis again increased by two
seconds and remains locked.
Inthe eventof twosuccessive retry attempts,the warm-uptime
willbeunlockedandsetto21seconds.Ifflameisthenachieved,
thewarm-up timewill beginadapting againwith 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 36E
manifold gas valve are opened. Flame must be detected within
4 seconds.
Ifflame isdetected, the delay-to-fan-onperiod begins.Afterthe
delay-to-fan-on period ends, the optional electronic air cleaner
is energized and the circulator fan is energized at heat speed.
Whenthethermostatissatisfied, the gasvalveisde-energized.
Afterproof of flameloss,the heat delay-to-fan-offperiodbegins
and the inducer blower remains energized to purge the system
for15seconds.Whenthepurgeiscomplete,theinducerblower
and humidifier are de-energized. After the delay-to-fan-off pe-
riod ends, the circulator fan and electronic air cleaner are de-
energized.
Ifflameisnotdetected,bothvalvesarede-energized,theignitor
is turned off, and the 50A55 control goes into the “retry” se-
quence.The“retry”sequenceprovidesa60-secondwaitfollow-
ing an unsuccessful ignition attempt (flame not detected). After
this wait, the ignition sequence is restarted with an additional 2
seconds of ignitor warm-up time. If this ignition attempt is
unsuccessful, one more retry will be made before the control
goes into system lockout.
If flame is detected, then lost, the 50A55 control will repeat the
initial ignition sequence for a total of four “recycles”. After four
unsuccessful “recycle” attempts, the control will go into system
lockout.
If flame is established for more than 10 seconds after ignition,
the 50A55 controller will clear the ignition attempt (or retry)
counter.Ifflameislostafter10seconds,itwillrestarttheignition
sequence. This can occur a maximum of five times before
system lockout.
During burner operation, a momentary loss of power of 50
milliseconds or longer will de-energize the main gas valve.
Whenpowerisrestored,thegasvalvewillremainde-energized
and a restart of the ignition sequence will begin immediately.
A momentary loss of gas supply, flame blowout, or a shorted or
openconditionintheflameprobecircuitwillbesensedwithin2.0
seconds. The gas valve will de-energize and the control will
restarttheignitionsequence.Recycleswillbeginandtheburner
will operate normally if the gas supply returns, or the fault
condition is corrected, before the last ignition attempt. Other-
wise, the control will go into system lockout.
Ifthecontrolhasgoneintosystemlockout,itmaybe 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 50A55 control and the
compressor. The cool delay-to-fan-on period begins. After the
delay period ends, the optional electronic air cleaner is ener-
gized,andthecirculatorfanisenergizedatcoolspeed.Afterthe
thermostat is satisfied, the compressor is de-energized and the
coolmodedelay-to-fan-offperiodbegins.Afterthedelay-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
circulatorfan(coolspeed)andoptionalelectronicaircleanerare
energized. When the fan switch is returned to the AUTO posi-
tion, the circulator fan and electronic air cleaner (optional) are
de-energized.
HEAT delay-
to-fan-off: Set switch #3 #4
60 sec.
90 sec.
120 sec.
180 sec.*
On On
Off On
On Off
Off Off
COOL delay-
to-fan-off: Set switch #1
45 sec.*
90 sec. On Off
HEAT delay-
to-fan-on: Set switch #2
30 sec.*
45 sec. On Off
OPTION SWITCH POSITIONS
* Factory setting

7
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 expires,
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.
Toassurepropercontrol operation,bothcontrolsmustshare
a common transformer ground (TR).
To enable twinning, do the following.
1. Power supplied to both furnaces must be from the same
phase of the incoming 120 VAC power.
2. Connect the TWIN screw terminals on the 50A55-843 of
the furnaces to be twinned to each other using a single
wire (14-22 AWG.).
SYSTEM LOCKOUT AND
DIAGNOSTIC FEATURES
SYSTEM LOCKOUT FEATURES
Whensystemlockoutoccurs,thegasvalveisde-energized,the
circulator blower is energized at heat speed, and, if flame is
sensed,the inducerbloweris energized.The diagnostic indica-
torlightwillflashorglowcontinuouslytoindicatesystemstatus.
(System lockout will never override the precautionary fea-
tures.)
To reset the control after system lockout, do one of the
following:
1. Interruptthecallforheatorcoolatthethermostatforatleast
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.Youmayalsoneedtoresettheflamerolloutsensor
switch.
3. Afteronehourinlockout,thecontrolwillautomaticallyreset
itself.
DIAGNOSTIC FEATURES
The50A55-843controlcontinuouslymonitorsits own operation
and the operation of the system. If a failure occurs, the LED will
indicateafailurecode asshownbelow.If thefailureisinternal
to the control, the light will stay on continuously. In this
case, the entire control should be replaced, as the control
is not field-repairable.
Ifthesensedfailureisin the system(externaltothecontrol),the
LEDwillflashinthefollowingflash-pausesequencestoindicate
failure status (each flash will last approximately 0.25 seconds,
and each pause will last approximately 2 seconds).
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
5 flashes, then pause Open rollout switch
6 flashes, then pause 115 Volt AC power reversed/Im-
proper ground
7 flashes, then pause Low flame sense signal
Continuous flashing Flame has been sensed when
(no pause) no flame should be present (no
call for heat)
The LED will also flash once at power-up.

MOUNTING HOLE TEMPLATE
FOR MOUNTING HOLE LOCATIONS
4.172 ±.007
(2 plcs.)
6.402 ±.010
(2 plcs.)
Refer to page 3 of the installation instructions for proper installation.
MOUNTING HOLE TEMPLATE