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50A65-843  
Universal Integrated Furnace Control  
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 50A65-843 is an automatic gas interrupted ignition control that employs a  
microprocessor to continually monitor, analyze, and control the proper opera-  
tion 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.  
These controls incorporate system fault analysis for quick gas flow shut-off,  
coupled with automatic ignition retry upon sensing a fault correction.  
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  
ordinances.  
Failure to comply with the following  
warnings could result in personal injury  
or property damage.  
This control is a precision instrument, and should be handled  
carefully. Rough handling or distorting components could cause  
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.  
• 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  
EXPLOSION HAZARD  
• Shut off main gas to appliance until installation is  
Description ........................................................ 1  
Precautions ....................................................... 1  
Specifications .................................................... 2  
Installation ......................................................... 3  
Mounting & Wiring  
complete.  
Operation .......................................................... 6  
Mounting Hole Template .................................... 8  
PART NO. 37-6270E  
Replaces 37-6270D  
0701  
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SPECIFICATIONS  
ELECTRICAL RATINGS [@ 77°F (25°C)]:  
TIMING SPECIFICATIONS  
(All times are in seconds, unless noted otherwise)  
Input Voltage: 25 VAC 50/60 Hz  
Max. Input Current @ 25 VAC: 0.45 amp  
Relay Load Ratings:  
50A65-843  
Valve Relay: 1.5 amp @ 25 VAC 50/60 Hz 0.6 pf  
Ignitor Relay: 2.0 amp @ 120 VAC 50/60 Hz  
(resistive)  
PRE-PURGE  
30  
20  
IGNITOR WARM-UP  
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  
1
4
TRIAL FOR IGNITION  
PERIOD  
*Measured with a DC microammeter in the flame probe lead  
RETRIES  
2 times  
12  
OPERATING TEMPERATURE RANGE:  
-40° to 175°F (-40° to 80°C)  
VALVE SEQUENCE PERIOD  
INTERPURGE  
60  
HUMIDITY RANGE:  
5% to 93% relative humidity (non-condensing)  
POST-PURGE  
15  
MOUNTING:  
LOCKOUT TIME  
300  
30, 45  
Surface mount multipoise  
HEAT DELAY-TO-FAN-ON*  
Timing Specs: (@ 60 Hz**)  
60/90/  
120/180  
HEAT DELAY-TO-FAN-OFF*  
maximum  
0.8 sec  
2.0 sec  
Flame Establishing Time:  
Flame Failure Response Time:  
COOL DELAY-TO-FAN-ON  
COOL DELAY-TO-FAN-OFF*  
AUTO RESET  
5
45, 90  
60 minutes  
YES  
** At 50 Hz, all timing specifications should be increased by  
20%  
Gases Approved: Natural, Manufactured, Mixed, Liquified  
HUMIDIFIER  
Petroleum, and LP Gas Air Mixtures are all approved for use.  
ELECTRONIC AIR CLEANER  
YES  
* 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.  
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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  
on the control’s terminations, system wiring harness or system  
• Do not exceed the specified voltage.  
• Replace existing control with exact model and  
dash number.  
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)  
#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 50A65 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 50A65 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 50A65 specification sheet for recommended terminals  
to mate with those on the control.  
Afterinstallationorreplacement,followappliancemanufacturer’s  
recommended installation or 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.  
The 50A65 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 50A65 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.  
Some applications may require connection to terminal E33  
located in the middle of the contol cover. If the control being  
replaced does not have this connection, it is not needed in the  
application and connection to terminal E33 is not required.  
Trane application - Jumper wire 151-2906 (provided with  
control) must be installed on the furnace from R01 to R02 of the  
12-pin connector.  
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TYPICAL SYSTEM WIRING DIAGRAM  
HOT  
(LINE)  
NEUTRAL  
(LINE)  
120 VAC  
24 VAC CLASS II  
TRANSFORMER  
TH  
24 VAC  
TR  
50A65-843  
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  
E33  
PRESSURE SWITCH (N. O.)  
PS  
HLI  
HLO  
FP  
FLAME  
SENSOR  
PROBE  
HIGH LIMIT  
(N. C.)  
AUX. HIGH  
LIMIT (N. C.)  
RO1  
GND  
RO2  
MV  
GAS  
VALVE  
MV  
TR  
TH  
LEGEND  
Low Voltage (24 VAC)  
Line Voltage (120 VAC)  
N. C. = Normally closed switch  
N. O. = Normally open switch  
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TYPICAL SYSTEM WIRING TABLE  
50A65  
TERMINAL  
TERMINAL  
SYSTEM COMPONENT  
TYPE  
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)  
W
G
R
Y
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  
rollout switch OUTPUT  
RO1  
RO2  
rollout switch INPUT  
(1 unused terminal)  
IND  
inducer HOT side  
4-pin  
IGN  
ignitor HOT side  
connector  
& harness  
IND N  
IGN N  
inducer NEUTRAL side  
ignitor NEUTRAL side  
COOL  
spade terminal  
spade terminal  
spade terminal  
spade terminal  
spade terminal  
spade terminal  
spade terminal  
spade terminal  
spade terminal  
spade terminal  
spade terminal  
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  
HEAT  
PARK (2 terminals)  
LINE  
XFMR  
EAC (optional)  
HUM (optional)  
CIR N  
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  
LINE N  
XFMR N  
EAC N (optional)  
HUM N (optional)  
E33  
3/16" spade terminal Auxiliary flame sense  
* maximum recommended flame probe wire length is 36 inches.  
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OPERATION  
OPTION SWITCHES  
The option switches on the 50A65-843 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.  
begins and the inducer blower remains energized to purge the  
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 50A65 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 again. 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  
45 sec.*  
90 sec.  
On  
Off  
If flame is detected, then lost, the 50A65 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.  
HEAT delay-  
to-fan-on:  
Set switch  
#2  
30 sec.*  
45 sec.  
On  
Off  
If flame is established for more than 10 seconds after ignition,  
the 50A65 controller will clear the ignition attempt (or retry)  
counter. If flame is lost after 10 seconds, it will restart the ignition  
sequence. Thiscanoccuramaximumof11timesbeforesystem  
lockout.  
HEAT delay-  
to-fan-off:  
Set switch  
#3  
#4  
60 sec.  
90 sec.  
120 sec.  
180 sec.*  
On  
Off  
On  
Off  
On  
On  
Off  
Off  
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.  
* Factory setting  
HEAT MODE  
If the control has gone into system lockout, it may be possible to  
reset the control by a momentary power interruption of ten  
seconds or longer. Refer to SYSTEM LOCKOUT FEATURES.  
In a typical system, a call for heat is initiated by closing the  
thermostat contacts. This starts the 50A65 control’s heating  
sequence. The inducer blower and optional humidifier are  
energized and the 768A silicon nitride ignitor is powered within  
one second.  
COOL MODE  
This control has an adaptive algorithm that reduces the ignitor  
temperature to slightly greater than the minimum temperature  
required to ignite gas in each particular application. The control  
measures the line voltage and determines an initial ignitor  
temperature setting based on the measurement. After each  
successful ignition, the control lowers the ignitor temperature  
slightly for the next ignition attempt. The control continues to  
lower the ignitor temperature until ignition does not occur, and  
thecontrolgoesintoretrymode. Forthesecondattempttoignite  
gaswithinthesamecallforheat,thecontrolincreasestheignitor  
temperature to the value it was on the third previous successful  
ignition. After ignition is successful, the control sets the ignition  
temperature at this value for the next 255 calls for heat, after  
which the control repeats the adaptive algorithm. The control is  
constantly making adjustments to the ignitor temperature to  
compensate for changes in the line voltage.  
In a typical system, a call for cool is initiated by closing the  
thermostat contacts. This energizes the 50A65 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, 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-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.  
The 80 VAC Silicon Nitride ignitor manufactured by White-  
Rodgers must be used. These ignitors are specially designed  
to operate with the 50A65’s adaptive ignition routine to ensure  
the most efficient ignitor temperature.  
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  
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DIAGNOSTIC FEATURES  
SYSTEM LOCKOUT AND  
DIAGNOSTIC FEATURES  
The 50A65-843 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.  
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 the precautionary fea-  
tures.)  
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).  
To reset the control after system lockout, do one of the  
following:  
1 flash, then pause  
System lockout  
2 flashes, then pause  
3 flashes, then pause  
4 flashes, then pause  
5 flashes, then pause  
6 flashes, then pause  
Pressure switch stuck closed  
Pressure switch stuck open  
Open limit switch  
Open rollout switch  
115 Volt AC power reversed/Im-  
proper ground  
Low flame sense signal  
Check ignitor  
Flame has been sensed when  
no flame should be present (no  
call for heat)  
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.  
7 flashes, then pause  
8 flashes, then pause  
Continuous flashing  
(no pause)  
3. After one hour in lockout, the control will automatically reset  
itself.  
The LED will also flash once at power-up.  
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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.