50A55-438
Integrated Furnace Control
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 50A55-438 is an automatic gas interrupted ignition control These controls incorporate system fault analysis for quick gas
that employs a microprocessor to continually monitor, analyze, flow shut-off, coupled with automatic ignition retry upon sensing
and control the proper operation of the gas burner, inducer, and a fault correction.
fan.
Signals interpreted during continual surveillance of the thermo-
stat and flame sensing element initiate automatic ignition of the
burner, sensing of the flame, and system shut-off during normal
operation.
PRECAUTIONS
Installation should be done by a qualified heating and air
conditioning contractor or licensed electrician.
WARNING
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
Failure to comply with the following
warnings could result in personal injury
or property damage.
ordinances.
This control is a precision instrument, and should be handled
carefully. Roughhandlingordistortingcomponentscouldcause
the control to malfunction.
FIRE HAZARD
Following installation or replacement, follow manufacturer’s
recommended installation/service instructions to ensure proper
operation.
• 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.).
• If the control has been in direct contact with water,
replace the control.
• Label all wires before disconnection when servic-
ing controls. Wiring errors can cause improper
and dangerous operation.
CAUTION
Do not short out terminals on gas valve or primary
control. Short or incorrect wiring may damage the
thermostat.
• 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.
CONTENTS
Description ............................................................. 1
Precautions ............................................................ 1
Specifications......................................................... 2
Installation.............................................................. 3
Mounting & Wiring
EXPLOSION HAZARD
• Shut off main gas to appliance until installation is
complete.
Operation ............................................................... 6
Mounting Hole Template........................................ 8
WHITE-RODGERS DIVISION
EMERSON ELECTRIC CO.
9797 REAVIS ROAD
ST. LOUIS, MISSOURI 63123-5398
PART NO. 37-6102B
Replaces 37-6102A
Printed in U.S.A.
0009
INSTALLATION
MOUNTING AND WIRING
All wiring should be installed according to local and national
electrical codes and ordinances.
WARNING
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.
FIRE HAZARD
When mounting the control, any orientation is acceptable.
Choose a location that will not damage, obstruct or place stress
• Do not exceed the specified voltage.
• Replace existing control with exact model and
dash number.
on the control’s terminations, system wiring harness or system
1
components. After finding a suitable location, drill four (4) ⁄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)
#8 sheet metal screws are provided to complete the installation.
• 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
Refer to the wiring diagram and wiring table when connecting
the 50A55 control to other components of the system.
UL approved, 105°C rated 18 gauge, stranded, 2⁄64” thick insula-
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.
• 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.
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 recommended terminals
to mate with those on the control.
The 50A55 has only one serviceable part–an automotive type
fuse, which protects the low voltage transformer from 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.
CAUTION
Do not short out terminals on gas valve or primary
control. Short or incorrect wiring may damage the
thermostat.
3
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
CIR N
LINE N
XFMR N
HUM N
EAC N
ELECTRONIC
AIR CLEANER
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
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
OPERATION
OPTION SWITCHES
The option switches on the 50A55-438 control are used to
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 positions.
system for 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.
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 SWITCH POSITIONS
COOL delay-
to-fan-off:
Set switch
#1
0 sec.
80 sec.
On
Off
If flame is detected, then lost, the 50A55 control will repeat the
initial ignition sequence for a total of ten “recycles”. After ten
unsuccessful “recycle” attempts, the control will go into system
lockout.
COOL delay-
to-fan-off:
Set switch
If flame is established for more than 10 seconds after ignition,
the 50A55 controller will clear the ignition attempt (or retry)
counter. If flame is lost after 10 seconds, it will restart the ignition
sequence. Thiscanoccuramaximumof11timesbeforesystem
lockout.
#2
#3
60 sec.
100 sec.
140 sec.
180 sec.
On
On
Off
Off
Off
On
On
Off
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 begin immediately.
HEAT MODE
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
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. Other-
wise, the control will go into system lockout.
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.
These controls have an adaptive algorithm that adjusts the
duration of the ignitor warm-up for the purpose of extending
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 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.
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
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).
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-off period begins. After the
optional delay-to-fan-off period ends, the circulator fan and
electronic air cleaner (optional) are de-energized.
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.
In the event of two successive retry attempts, the warm-up time
willbeunlockedandsetto21seconds. Ifflameisthenachieved,
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.
MANUAL FAN ON MODE
If the thermostat fan switch is moved to the ON position, the
circulatorfan(heatspeed)andoptionalelectronicaircleanerare
energized. When the fan switch is returned to the AUTO posi-
tion, the circulator fan and electronic air cleaner (optional) are
de-energized.
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, the circulator fan
is energized at heat speed. If there is an optional electronic air
cleaner on the system, the electronic air cleaner is also ener-
gized. When the thermostat is satisfied, the gas valve is de-
energized. After proof of flame loss, the delay-to-fan-off period
begins and the inducer blower remains energized to purge the
6
DIAGNOSTIC FEATURES
SYSTEM LOCKOUT AND
DIAGNOSTIC FEATURES
The 50A55 control continuously monitors its own operation 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 shown below. If the failure is internal
to the control, the light will stay on continuously. In this
case, the entire control should be replaced, as the control
isnotfield-repairable. IftheLEDiscontinuouslyoff, theremay
be no power to the control; the fuse on the control may be open;
or there may be a failure in the control.
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 indica-
tor light will flash or glow continuously to indicate system status.
(System lockout will never override any precautionary
features.)
To reset the control after system lockout, do one of the
following:
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).
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 flashes, then pause
3 flashes, then pause
4 flashes, then pause
5 flashes, then pause
6 flashes, then pause
System lockout (no flame)
Pressure switch problem
Thermal protection device open
Flame sensed with gas valve off
115 Volt AC power reversed/im-
proper ground
2. Interrupt the 24 VAC power at the control for at least one
second.Youmayalsoneedtoresettheflamerolloutsensor
switch.
3. Afteronehourinlockout, thecontrolwillautomaticallyreset
itself.
7 flashes, then pause
8 flashes, then pause
Gas valve circuit error
Low flame sense signal
The LED will also flash once at power-up.
7
MOUNTING HOLE TEMPLATE
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.
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