Universal Integrated Furnace Control
INSTALLATION INSTRUCTIONS
Operator: Save these instructions for future use!
FAILURE TO READ AND FOLLOW ALL INSTRUCTIONS CAREFULLY BEFORE
INSTALLING OR OPERATING THIS CONTROL COULD CAUSE PERSONAL
INJURY AND/OR PROPERTY DAMAGE.
The 50A55-843 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.
TRANE APPLICATION - Installer MUST read page 3 “Mounting and Wiring”
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 conditioning contractor or licensed electrician.
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 components could cause
the control to malfunction.
Following installation or replacement, follow manufacturer’s
recommended installation/service instructions to ensure proper
operation.
CAUTION
Do not short out terminals on gas valve or primary
control. Short or incorrect wiring may damage the
thermostat.
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
flow shut-off, coupled with automatic ignition retry upon sensing
a fault correction.
Failure to comply with the following
warnings could result in personal injury
or property damage.
FIRE HAZARD
• Do not exceed the specified voltage.
• 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 servicing 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.
50A55-843
DESCRIPTION
PRECAUTIONS
WARNING
White-Rodgers is a division
of Emerson Electric Co.
www.white-rodgers.com
PART NO. 37-6265G
Replaces 37-6265F
0526
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.
(All times are in seconds, unless noted otherwise)
TIMING SPECIFICATIONS
50A55-843
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
30
17
5
21
1
4
2 times
12
60
15
300
30, 45
60/90/
120/180
5
45, 90
60 minutes
HUMIDIFIER
ELECTRONIC AIR CLEANER
* These times will vary depending on
option switch position. The control is
factory-set at 30 seconds heat delayto-fan-on, 180 seconds heat delay-tofan-off and 45 seconds cool delay-tofan-off. See OPERATION section for
further information.
YES
YES
2
WARNING
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 servicing 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.
CAUTION
Do not short out terminals on gas valve or primary
control. Short or incorrect wiring may damage the
thermostat.
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 minimum ambient temperatures of -40°F.
When mounting the control, any orientation is acceptable.
Choose a location that will not damage, obstruct or 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
harness or other system components are not damaged. Four (4)
#8 sheet metal screws are provided to complete the installation.
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,
tion 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 recommended terminals
to mate with those on the control.
After installation or replacement, follow appliance manufacturer’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
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.
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.
Amana/Goodman application - 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.
2
¦64” thick insula-
Trane application - Jumper wire 151-2906 (provided with
control) must be installed on the furnace from R01 to R02 of the
12-pin connector.
3
HOT
(LINE)
TYPICAL SYSTEM WIRING DIAGRAM
120 VAC
24 VAC CLASS II
TRANSFORMER
24 VAC
TH TR
50A55
COOL
HEAT
PARK
PARK
LINE
XFMR
EAC
HUM
NEUTRAL
(LINE)
CIRCULATOR
BLOWER
HUMIDIFIER
ELECTRONIC
AIR CLEANER
FLAME
SENSOR
PROBE
INDUCER
50A55-843
in other
furnace(s)
—
TWINNING
APPLICATIONS
ONLY
IND
IGN
IND N
IGN N
CIR N
LINE N
XFMR N
HUM N
EAC N
Y
W
G
R
C
TWIN*TWIN*
PS
HLI
HLO
FP
RO1
GND
RO2
MV
MV
TR
TH
IGNITOR
Y
W
G
R
THERMOSTAT
PRESSURE SWITCH (N. O.)
HIGH LIMIT
(N. C.)
ROLLOUT
(N. C.)
COMPRESSOR
CONTACTOR
AUX. HIGH
LIMIT (N. C.)
GAS
VALVE
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
W
G
R
Y
C
TWIN*
MV (2 terminals)
TR
TH
RO1
RO2
FP
PS
HLI
HLO
GND
(unused terminal)
TERMINAL
TYPE
Terminal
block with
captive
screws
12-pin
connector
& harness
SYSTEM COMPONENT
CONNECTION
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
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)
* 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.
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
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
5
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-tofan-on and heat delay-to-fan-off periods. The following table
shows the time periods that will result from the various switch
positions.
OPTION SWITCH POSITIONS
COOL delay-
to-fan-off:
45 sec.*
90 sec.
HEAT delay-
to-fan-on:
30 sec.*
45 sec.
HEAT delay-
to-fan-off:
60 sec.
90 sec.
120 sec.
180 sec.*
* Factory setting
Set switch
#1
On
Off
Set switch
#2
On
Off
Set switch
#3 #4
On On
Off On
On Off
Off Off
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 duration 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
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.
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 ontime will continue until flame fails to be achieved (resulting in a
retry).
In the event of a retry, the warm-up time will be increased by two
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 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
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.
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 optional electronic air cleaner
is energized and the circulator fan is energized at heat speed.
When the thermostat is satisfied, the gas valve 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 deenergized.
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 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. If flame is lost after 10 seconds, it will restart the ignition
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.
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-energize and the control will
restart the ignition sequence. Recycles 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.
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 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 satisfied, the compressor is de-energized and the
cool mode delay-to-fan-off period begins. After the delay-to-fanoff 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
circulator fan (cool 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.
6
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.
To assure proper control operation, both controls must share
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
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 50A55-843 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 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
is not field-repairable.
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 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.
The Emerson logo is a
trademark and a service mark
of Emerson Electric Co.
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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