50A55-474 & 50A55-571
Integrated Furnace Controls
WHITE-RODGERS
INSTALLATION INSTRUCTIONS
Operator: Save these instructions for future use!
FAILURETOREADANDFOLLOWALLINSTRUCTIONSCAREFULLYBEFORE
INSTALLING OR OPERATING THIS CONTROL COULD CAUSE PERSONAL
INJURY AND/OR PROPERTY DAMAGE.
DESCRIPTION
The 50A55-474 and 50A55-571 are automatic gas inter-
rupted ignition controls that employ a microprocessor to
continually monitor, analyze, and control the proper op-
eration 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.
Thesecontrolsincorporatesystemfaultanalysisforquick
gas flow shut-off, coupled with automatic ignition retry
upon sensing a fault correction.
PRECAUTIONS
CAUTION
GENERAL PRECAUTION
!
!
To prevent electrical shock and/or equipment
damage, disconnect electric power to system at
main fuse or circuit breaker box until installation
is complete.
Application of this type of control may cause
flame rollout on initial start-up and could cause
personal injury and/or property damage.
Replace only with exact model number, includ-
ing dash number. Failure to use exact replace-
ment control could cause personal injury and/or
property damage.
Label all wires prior to disconnection when ser-
vicing controls. Wiring errors can cause im-
proper and dangerous operation.
This control is not intended for use in locations
where it may come in contact with water. Suit-
able protection must be provided to shield the
control from exposure to water (dripping, spray-
ing, rain, etc.).
Ifindoubtaboutwhetheryourwiringismillivolt,line,orlow
voltage, have it inspected by a qualified heating and air
conditioning contractor or licensed electrician.
Do not exceed the specification ratings.
All wiring must conform to local and national electrical
codes and ordinances.
WARNING
!
Do not use on circuits exceeding specified volt-
age. Higher voltage will damage control and
could cause shock or fire hazard.
This control is a precision instrument, and should be
handled carefully. Rough handling or distorting compo-
nents could cause the control to malfunction.
CONTENTS
Do not short out terminals on gas valve or pri-
marycontroltotest. Shortorincorrectwiringwill
damage thermostat and could cause personal
injury and/or property damage.
Description ......................................................... 1
Precautions ........................................................ 1
Specifications..................................................... 2
Installation.......................................................... 3
Mounting & Wiring
Operation ........................................................... 6
WHITE-RODGERS DIVISION
EMERSON ELECTRIC CO.
9797 REAVIS ROAD
ST. LOUIS, MISSOURI 63123-5398
PART NO. 37-5800C
Replaces 37-5800B
Printed in U.S.A.
9751
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INSTALLATION
MOUNTING AND WIRING
WARNING
NOTE
All wiring should be installed according to local and
national electrical codes and ordinances.
!
Do not use on circuits exceeding specified volt-
age. Higher voltage will damage control and
could cause shock or fire hazard.
The control must be secured to an area that will experi-
ence a minimum of vibration and remain below the maxi-
mum ambient temperature rating of 175°F. The control is
approved for minimum ambient temperatures of -40°F.
Any orientation is acceptable.
CAUTION
!
Refer to the wiring diagram and wiring table when con-
necting the 50A55 control to other components of the
system.
UL approved, 105°C rated 18 gauge, stranded, 2⁄64” thick
insulation wire is recommended for all low voltage safety
circuit connections. Refer to 50A55 specification sheet
for recommended terminals to mate with those on the
control.
UL approved 105°C rated 16 gauge min., stranded, 4⁄64”
thick insulation wire is recommended for all line voltage
connections. Refer to 50A55 specification sheet for rec-
ommended terminals to mate with those on the control.
To prevent electrical shock and/or equipment
damage, disconnect electric power to system at
main fuse or circuit breaker box until installation
is complete. Failure to earth ground the appli-
ance or reversing the neutral and hot wire con-
nection to the line can cause shock hazard.
Shut off main gas to heating system until instal-
lation is complete.
Route and secure all wiring as far from flame
as practical to prevent fire and/or equipment
damage.
The 50A55 has only one serviceable part–an automotive
typefuse,whichprotectsthelowvoltagetransformerfrom
damage if its 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 is not the cause of the control’s problem,
replace the entire 50A55 control. There are no other user
serviceable parts.
3
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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
CIRCU-
LATOR
BLOWER
XFMR
EAC
HUM
IND
IGN
IND N
IGN N
INDUCER
IGNITOR
HUMIDIFIER
(-474 only)
CIR N
LINE N
XFMR N
HUM N
EAC N
ELECTRONIC
AIR CLEANER
(-474 only)
Y
W
G
R
C
Y
W
G
R
COMPRESSOR
CONTACTOR
THERMOSTAT
PRESSURE SWITCH (N. O.)
PS
HLI
HLO
FP
FLAME
SENSOR
PROBE
HIGH LIMIT
(N. C.)
AUX. HIGH
LIMIT (N. C.)
GND
GAS
VALVE
MV
MV
TR
TH
LEGEND
Low Voltage (24 VAC)
Line Voltage (120 VAC)
N. C. = Normally closed switch
N. O. = Normally open switch
4
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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
gas valve (both gas solenoids are connected in parallel)
24 VAC transformer (low voltage COMMON side)
24 VAC transformer (low voltage HIGH side)
flame sensor probe*
MV (2 terminals)
TR
TH
FP
12-pin
PS
connector
& harness
pressure switch INPUT
HLI
high limit INPUT
HLO
high limit OUTPUT
GND
MUST BE RELIABLY GROUNDED TO CHASSIS
(3 unused terminals)
IND
inducer HOT side
IGN
4-pin
connector
& harness
ignitor HOT side
IND N
IGN N
COOL
HEAT
inducer NEUTRAL side
ignitor NEUTRAL side
spade terminal circulator blower COOL SPEED terminal
spade terminal circulator blower HEAT SPEED terminal
PARK (2 terminals) spade terminal unused circulator blower terminals
LINE
spade terminal input voltage (120 VAC) HOT side
spade terminal 24 VAC transformer line voltage HOT side
spade terminal humidifier HOT side
XFMR
HUM (optional)
EAC (optional)
CIR N
spade terminal electronic air cleaner HOT side
spade terminal circulator blower NEUTRAL terminal
spade terminal input voltage (120 VAC) NEUTRAL side
spade terminal 24 VAC transformer line voltage NEUTRAL side
spade terminal humidifier NEUTRAL side
LINE N
XFMR N
HUM N (optional)
EAC N (optional)
spade terminal electronic air cleaner NEUTRAL side
* maximum recommended flame probe wire length is 36 inches.
5
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OPERATION
OPTION SWITCHES
Upon a call for heat, if the warm-up time has not been
locked, it will be decreased by one second. This reduction
of the ignitor on-time will continue until flame fails to be
achieved (resulting in a retry).
(50A55-474 only)
Theoptionswitchesonthe50A55-474controlareusedto
determine the length of the cool delay-to-fan-off and heat
delay-to-fan-off periods. The following tables show the
time periods that will result from the various switch posi-
tions.
In the event of a retry, the warm-up time will be increased
by two seconds and locked 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
is again increased by two seconds and remains locked.
OPTION SWITCH POSITIONS
In the event of two successive retry attempts, the warm-
up time will be unlocked and set to 21 seconds. If flame is
then achieved, the warm-up time will begin adapting
again with the next call for heat. If, however, this third
attempt fails to achieve flame, the control will go into
system lockout.
COOL delay-
to-fan-off:
Set switch
#1
0 sec.
80 sec.
On
Off
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. If flame is detected, the delay-
to-fan-on period begins. After the delay-to-fan-on period
ends, thecirculatorfanisenergizedatheatspeed. Ifthere
is an optional electronic air cleaner on the system, the
electronicaircleanerisalsoenergized. Whenthethermo-
stat is satisfied, the gas valve is de-energized. After proof
of flame loss, the delay-to-fan-off period begins and the
inducerblowerremainsenergizedtopurgethesystemfor
5 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. If flame is not detected, both
valves are de-energized, the ignitor is turned off, and the
50A55 control goes into the “retry” sequence.
COOL delay-
to-fan-off:
Set switch
#2
#3
60 sec.
100 sec.
140 sec.
180 sec.
On
On
Off
Off
Off
On
On
Off
OPTION JUMPER
(50A55-571 only)
The option jumper on the 50A55-571 control is used to
determine the length of the cool delay-to-fan-off period.
The following table shows the time periods that will result
from the various jumper conditions.
The “retry” sequence provides a 60-second wait following
an unsuccessful ignition attempt (flame not detected).
After this wait, the ignition sequence is restarted with 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.
OPTION JUMPER CONDITION
COOL delay-
to-fan-off:
Jumper
Condition
0 sec.
Installed
80 sec.
Clipped (open)
Ifflameisdetected,thenlost,the50A55controlwillrepeat
the initial ignition sequence for a total of ten “recycles”.
After ten unsuccessful “recycle” attempts, the control will
go into system lockout.
HEAT MODE
In a typical system, a call for heat is initiated by closing the
thermostat contacts. This starts the 50A55 control’s heat-
ing sequence. The inducer blower and optional humidifier
are energized and the ignitor is powered within one
second.
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. This can occur a maximum
of 11 times before system lockout.
These controls have an adaptive algorithm that adjusts
the duration of the ignitor warm-up for the purpose of
extendingignitorlife. Uponinitialapplicationofpower, the
warm-up time is 17 seconds. The ignitor on-time will then
be increased or decreased depending on whether or not
flame is achieved. The warm-up time is limited 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.
Duringburneroperation, amomentarylossofpowerof50
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 2.0 seconds. The gas valve will de-ener-
6
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gize and the control will restart the ignition sequence. A
recycle will begin and the burner will operate normally if
the gas supply returns, or the fault condition is corrected,
before the last ignition attempt. Otherwise, the control will
go into system lockout.
DIAGNOSTIC FEATURES
The 50A55 control continuously monitors its own opera-
tion and the operation of the system. The LED light on the
control will flash slowly (one flash per second) if there are
no failures and no call for heat. If there is a call for heat,
the LED will flash quickly (one flash per half-second). If a
failure occurs, the LED will indicate a failure code as
shownbelow. Ifthefailureisinternaltothecontrol, the
light will stay on continuously. In this case, the entire
control should be replaced, as the control is not field-
repairable.IftheLEDiscontinuouslyoff,theremaybeno
power to the control; the fuse on the control may be open;
or there may be a failure in the control.
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 50A55 control.
The compressor and optional electronic air cleaner are
energized, and the circulator fan is energized at cool
speed. After the thermostat is satisfied, the compressor is
de-energized and the (optional) cool mode delay-to-fan-
offperiodbegins.Aftertheoptionaldelay-to-fan-offperiod
ends, the circulator fan and electronic air cleaner (op-
tional) are de-energized.
If the sensed failure is in the system (external to the
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 flashes, then pause Systemlockout(noflame)/check
line polarity
3 flashes, then pause Pressure switch problem
4 flashes, then pause Thermal protection device open
5 flashes, then pause Flame sensed with gas valve off
6 flashes, then pause 115 Volt AC power reversed
7 flashes, then pause Gas valve circuit error
8 flashes, then pause Low flame sense signal
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.
The LED will also flash once at power-up.
SYSTEM LOCKOUT AND
DIAGNOSTIC FEATURES
SYSTEM LOCKOUT FEATURES
When system lockout occurs, the gas valve is de-ener-
gized, 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 continu-
ously to indicate system status. (System lockout will
never override any precautionary features.)
Toresetthecontrolaftersystemlockout, dooneofthe
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, interrupt-
ing 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. Afteronehourinlockout,thecontrolwillautomatically
reset itself.
7
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