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50A55-286  
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 50A55-286 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.  
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.  
PART NO. 37-6101A  
Printed in U.S.A.  
9797 REAVIS ROAD  
9919  
ST. LOUIS, MISSOURI 63123-5398  
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SPECIFICATIONS  
ELECTRICAL RATINGS [@ 77°F (25°C)]:  
Input Voltage: 25 VAC 50/60 Hz  
TIMING SPECIFICATIONS  
(All times are in seconds, unless noted otherwise)  
Max. Input Current @ 25 VAC: 0.45 amp  
Relay Load Ratings:  
50A55-286  
Valve Relay: 1.5 amp @ 25 VAC 50/60 Hz 0.6 pf  
Ignitor Relay: 6.0 amp @ 120 VAC 50/60 Hz  
(resistive)  
PRE-PURGE  
0
INITIAL IGNITOR  
RETRY IGNITOR  
17  
28  
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  
IGNITION ACTIVATION  
PERIOD  
5
*Measured with a DC microammeter in the flame probe  
lead  
TRIAL FOR IGNITION  
PERIOD  
7
2 times  
21  
RETRIES  
OPERATING TEMPERATURE RANGE:  
VALVE SEQUENCE  
PERIOD  
-40° to 175°F (-40° to 80°C)  
HUMIDITY RANGE:  
15  
15  
INTERPURGE  
5% to 93% relative humidity (non-condensing)  
POST-PURGE  
MOUNTING:  
200  
30  
LOCKOUT TIME  
DELAY TO HEAT ON  
Surface mount multipoise  
Timing Specs: (@ 60 Hz**)  
60/90/  
120/180  
DELAY TO HEAT OFF*  
maximum  
Flame Establishing Time:  
Flame Failure Response Time:  
0.8 sec  
2.0 sec  
0
45  
DELAY TO COOL ON  
DELAY TO COOL OFF  
AUTO RESET  
** At 50 Hz, all timing specifications should be increased  
by 20%  
60 minutes  
YES  
HUMIDIFIER  
Gases Approved: Natural, Manufactured, Mixed, Liquid  
Petroleum, and LP Gas Air Mixtures are all approved for  
use.  
ELECTRONIC AIR  
CLEANER  
YES  
* This time will vary depending on option switch  
position. The control is factory-set at 60 sec.  
delay to heat off. See OPERATION section  
for further information.  
2
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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  
voltage. 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.  
Whenmountingthecontrol, anyorientationisacceptable.  
Choose a location that will not damage, obstruct or place  
stress on the control’s terminations, system wiring har-  
ness or system components. After finding a suitable  
CAUTION  
!
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.  
1
location, drill four (4) 8” holes for mounting control. To  
ensurepropermountingholelocations, thereisa mount-  
ing 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 har-  
ness or other system components are not damaged. Four  
(4) #8 sheet metal screws are provided to complete the  
installation.  
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.  
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, 264” 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.  
To prevent damage to the transformer, system  
components or wiring harness, take care when  
drillingnewmountingholes.Failuretodosomay  
result in electrical shock, fire hazard or equip-  
ment damage.  
UL approved 105°C rated 16 gauge min., stranded, 464”  
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.  
After installation or replacement, follow appliance  
manufacturer’s recommended installation or service in-  
structions to ensure proper operation.  
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  
CIRCULATOR  
BLOWER  
XFMR  
EAC  
HUM  
INDUCER  
IGNITOR  
IND  
IGN  
IGN N  
HUMIDIFIER  
IND N  
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  
RO1  
GND  
RO2  
MV  
FLAME  
SENSOR  
PROBE  
HIGH LIMIT  
(N. C.)  
AUX. HIGH  
LIMIT (N. C.)  
THERMAL  
ROLLOUT (N. C.)  
GAS  
VALVE  
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)  
rollout switch OUTPUT  
MV (2 terminals)  
TR  
TH  
RO1  
RO2  
12-pin  
rollout switch INPUT  
FP  
connector  
& harness  
flame sensor probe*  
PS  
pressure switch INPUT  
HLI  
high limit INPUT  
HLO  
high limit OUTPUT  
GND  
(unused terminal)  
IND  
MUST BE RELIABLY GROUNDED TO CHASSIS  
inducer HOT side  
4-pin  
IGN  
ignitor HOT side  
connector  
& harness  
IND N  
IGN N  
COOL  
HEAT  
inducer NEUTRAL side  
ignitor NEUTRAL side  
1
1
1
⁄ ” spade terminal  
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  
4
⁄ ” spade terminal  
4
PARK (2 terminals) ⁄ ” spade terminal  
4
1
LINE  
⁄ ” spade terminal  
4
1
1
1
1
1
1
1
1
XFMR  
⁄ ” spade terminal  
4
EAC (optional)  
HUM (optional)  
CIR N  
⁄ ” spade terminal  
4
⁄ ” spade terminal  
4
⁄ ” spade terminal  
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  
4
LINE N  
⁄ ” spade terminal  
4
XFMR N  
⁄ ” spade terminal  
4
EAC N (optional)  
HUM N (optional)  
⁄ ” spade terminal  
4
⁄ ” spade terminal  
4
* maximum recommended flame probe wire length is 36 inches.  
5
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OPERATION  
OPTION SWITCHES  
Ifflameisdetected,thenlost,the50A55controlwillrepeat  
the initial ignition sequence for a total of four “recycles”.  
Theoptionswitchesonthe50A55-286controlareusedto After four unsuccessful “recycle” attempts, the control will  
determine the length of the heat delay-to-fan-off periods. go into system lockout.  
The following table shows the time periods that will result  
from the various switch positions.  
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 five times before system lockout.  
OPTION SWITCH POSITIONS  
HEAT delay-  
to-fan-off:  
Set switch  
#1  
#2  
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.  
60 sec.*  
90 sec.  
120 sec.  
180 sec.  
On  
Off  
On  
Off  
On  
On  
Off  
Off  
*Factory set position  
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-  
gize and the control will restart the ignition sequence.  
Recycles will begin and the burner will operate normally  
ifthegassupplyreturns,orthefaultconditioniscorrected,  
before the last ignition attempt. Otherwise, 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.  
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.  
Theignitoristhenallowedtowarmupfor17seconds.The  
120 VAC ignitors with a 17 second warm-up time  
manufacturedbyCarborundum,IgnitorSystems,Inc.,  
or Norton must be used. These ignitors are specially  
designed to heat up quickly at a low voltage condition  
without overheating at a high voltage condition.  
COOL MODE  
At the end of the ignitor warm-up time, both valves in the  
36E manifold gas valve are opened. Flame must be  
detected within 7 seconds.  
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 cool mode delay-to-fan-off period  
begins. After the cool delay-to-fan-off period ends, the  
circulator fan and electronic air cleaner are de-energized.  
If flame is detected, the delay-to-fan-on period begins.  
After the delay-to-fan-on period ends, the optional elec-  
tronic air cleaner is powered and the circulator fan is  
energized at heat speed. When the thermostat is satis-  
fied, the gas valve is de-energized. After proof of flame  
loss, the heat delay-to-fan-off period begins and the  
inducerblowerremainsenergizedtopurgethesystemfor  
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.  
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.  
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 15-  
second wait following an unsuccessful ignition attempt  
(flame not detected). After this wait, the ignition sequence  
is restarted with an additional 11 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.  
6
DIAGNOSTIC FEATURES  
SYSTEM LOCKOUT AND  
DIAGNOSTIC FEATURES  
The 50A55 control continuously monitors its own opera-  
tionandtheoperationofthesystem.Ifafailureoccurs,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.  
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. If the sensed failure is in the system (external to the  
The diagnostic indicator light will flash or glow continu- control), the LED will flash in the following flash-pause  
ously to indicate system status. (System lockout will sequences to indicate failure status (each flash will last  
never override the precautionary features.)  
approximately 0.25 seconds, and each pause will last  
approximately 2 seconds). If more than one failure is  
detected, the LED will alternate through all the failure  
codes that apply.  
Toresetthecontrolaftersystemlockout, dooneofthe  
following:  
1. Interrupt the call for heat or cool at the thermostat for  
atleastonesecond,butlessthan20seconds(ifflame  
is sensed with the gas valve de-energized, interrupt-  
ing the call for heat at the thermostat will not reset the  
control).  
Continuous flashing  
(no pause)  
Low flame sense signal  
1 flash, then pause  
Lockoutcausedbyflamesensed  
when there should be no flame  
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.  
2 flashes, then pause Pressure switch stuck closed  
3 flashes, then pause Pressure switch stuck open  
4 flashes, then pause High limit open  
5 flashes, then pause Rollout switch open or rollout  
sensed  
3. Afteronehourinlockout,thecontrolwillautomatically  
reset itself.  
6 flashes, then pause *Lockout caused by pressure  
switch opening 4 times in one  
cycle  
7 flashes, then pause *Lockout caused by no ignition  
(after 3 trials)  
8 flashes, then pause *Lockoutcausedbylossofflame  
5 times in one heating cycle  
9 flashes, then pause 115 Volt AC power reversed/  
improper ground  
12 flashes, then pause Ignitor relay sense error  
The LED will also flash once at power-up.  
* Will automatically restart from lockout after one hour. All  
other conditions need to be cleared for the control to  
resume normal operation.  
7
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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.