White Rodgers 50A66 743 Thermostat User Manual

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50A66-743  
Integrated Furnace Control  
INSTALLATION INSTRUCTIONS  
Operator: Save these instructions for future use!  
FAILURETO READ AND FOLLOW ALL INSTRUCTIONS CAREFULLY BEFORE  
INSTALLING OR OPERATING THIS CONTROL COULD CAUSE PERSONAL  
INJURY AND/OR PROPERTY DAMAGE.  
DESCRIPTION  
50A66-743 Cross Reference Information  
The 50A66-743 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.  
Lennox  
23W51  
White-Rodgers  
100925-01  
100925-02  
100925-03  
17W92  
69M0801  
69M15  
50A66-122  
50A66-123  
50A66-743  
Signalsinterpretedduringcontinualsurveillanceofthethermostat  
and flame sensing element initiate automatic ignition of the  
burner, sensing of the flame, and system shut-off during normal  
operation.  
23W5101  
30W25  
69M1501  
30W2501  
69M08  
17W9201  
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  
Ifindoubtaboutwhetheryourwiringismillivolt,line,orlowvoltage,  
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.  
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  
• Do not exceed the specified voltage.  
• Replaceexistingcontrolwithexactmodelanddash  
number.  
Following installation or replacement, follow manufacturer’s  
recommended installation/service instructions to ensure proper  
operation.  
• 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.  
• Labelallwiresbeforedisconnectionwhenservicing  
controls. Wiring errors can cause improper and  
dangerous operation.  
CAUTION  
Donotshortoutterminalsongasvalveorprimary  
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  
System Lockout and Diagnostic Features........... 7  
Troubleshooting................................................... 8  
PART NO. 37-7473A  
1313  
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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:  
OPERATING TEMPERATURE RANGE:  
-40° to 175°F (-40° to 80°C)  
HUMIDITY RANGE:  
5% to 93% relative humidity (non-condensing)  
Valve Relay: 1.5 amp @ 25 VAC 50/60 Hz 0.6 pf MOUNTING:  
Ignitor Relay: 2.0 amp @ 120 VAC 50/60 Hz  
(resistive)  
Surface mount multipoise  
Timing Specs: (@ 60 Hz**)  
Inducer Relay: 2.2 FLA–3.5 LRA @ 120 VAC  
Circulator Relay: 14.5 FLA–25.0 LRA @ 120 VAC  
Flame Current Requirements:  
maximum  
Flame Establishing Time:  
Flame Failure Response Time:  
0.8 sec  
2.0 sec  
** At 50 Hz, all timing specifications should be increased  
by 20%  
Minimumcurrenttoinsureamedetection:0.25µaDC*  
Maximum current for non-detection: 0.1 µa DC*  
Maximum allowable leakage resistance:100 M ohms GasesApproved:Natural,Manufactured,Mixed,Liquified  
Petroleum,andLPGasAirMixturesareallapprovedforuse.  
*MeasuredwithaDCmicroammeterintheameprobelead  
TIMING SPECIFICATIONS  
(All times are in seconds, unless noted otherwise  
Event  
Pre-Purge  
Definition  
50A66-743  
The period of time intended to allow for the dissipation of any unburned  
gas or residual products of combustion at the beginning of a furnace  
operating cycle prior to initiating ignition  
15  
The period of time between initiation of gas flow and the action to  
shut off the gas flow in the event of failure to establish proof of the  
supervised ignition source or the supervised main burner flame.  
The period of time between energizing the main gas valve and  
deactivation of the ignition means prior to the end of TFI  
Trial for Ignition  
Period (TFI)  
4
Ignition Activation  
Period (IAP)  
Retries  
4
The additional attempts within the same thermostat cycle for ignition  
when the supervised main burner flame is not proven within the first  
trial for ignition period.  
4 times  
Valve sequence period equals 4 seconds trial for ignition period x  
(1 initial try + 2 retries) + 12 seconds.  
Valve Sequence  
Period  
Interpurge  
20  
15  
The period of time intended to allow for the dissipation of any unburned  
gas or residual products of combustion between the failed trial for  
ignition and the retry period.  
The period of time intended to allow for the dissipation of any unburned  
gas or residual products of combustion at the end of a furnace burner  
operating cycle. Post-purge begins at the loss of flame sense.  
ANSI standard rated module timing.  
Post-Purge  
5
Lockout Time  
250  
45  
The period of time between proof of the supervised main burner flame  
and the activation of the blower motor at Heat speed.  
The period of time between the loss of a call for heat and the  
deactivation of the blower motor at Heat speed.  
Heat Delay-To-Fan-On  
Heat Delay-To-Fan-Off*  
Cool Delay-To-Fan-On  
Cool Delay-To-Fan-Off*  
Ignitor Warm-up  
60/90/120/180  
The period of time after a thermostat demand for cool before energizing  
the circulator blower motor at Cool speed.  
The period of time between the loss of a call for cool and the  
deactivation of the blower motor at Cool speed.  
The length of time allowed for the igniter to heat up prior to the initiation  
of gas flow.  
2
2/45  
20  
After one (1) hour of internal or external lockout, the control will auto-  
matically reset itself and go into an auto restart purge for 60 seconds.  
Auto Reset  
60 minutes  
Humidifier  
Yes  
Yes  
Electronic Air Cleaner  
*This time will vary depending on option switch position. The control is factory set at 90 seconds HEAT  
delay-to-fan-off and 45 seconds COOL delay-to-fan-off. See OPERATION section for further information.  
2
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INSTALLATION  
WARNING  
Donotshortoutterminalsongasvalveorprimary  
control. Short or incorrect wiring may damage  
the thermostat.  
FIRE HAZARD  
• Do not exceed the specified voltage.  
• Replaceexistingcontrolwithexactmodelanddash  
number.  
• Protect the control from direct contact with water  
(dripping, spraying, rain, etc.).  
• Labelallwiresbeforedisconnectionwhenservicing  
controls. Wiring errors can cause improper and  
dangerous operation.  
MOUNTING AND WIRING  
All wiring should be installed according to local and na-  
tional electrical codes and ordinances.  
Thecontrolmustbesecuredtoanareathatwillexperience  
a minimum of vibration and remain below the maximum  
ambient temperature rating of 175°F. The control is ap-  
proved for minimum ambient temperatures of -40°F.  
• Route and secure wiring away from flame.  
Any orientation is acceptable.  
SHOCK HAZARD  
Refertothewiringdiagramandwiringtablewhenconnect-  
ing the 50A66 control to other components of the system.  
• Disconnect electric power before servicing .  
• Ensure proper earth grounding of appliance.  
• Ensure proper connection of line neutral and line  
hot wires.  
2
64  
UL approved, 105°C rated 18 gauge, stranded, / ” thick  
insulation wire is recommended for all low voltage safety  
circuit connections.Refer to 50A66 specification sheet for  
recommendedterminalstomatewiththoseonthecontrol.  
4
EXPLOSION HAZARD  
• Shut off main gas to appliance until installation is  
complete.  
64  
UL approved 105°C rated 16 gauge min., stranded, / ”  
thick insulation wire is recommended for all line voltage  
connections. Refer to 50A66 specification sheet for rec-  
ommended terminals to mate with those on the control.  
After installation or replacement, follow appliance manu-  
facturer’srecommendedinstallationorserviceinstructions  
to ensure proper operation.  
3
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WIRING  
TYPICAL SYSTEM WIRING DIAGRAM  
HOT  
(LINE)  
NEUTRAL  
(LINE)  
120 VAC  
24 VAC CLASS II  
TRANSFORMER  
TH  
24 VAC  
50A66  
TR  
FAN  
COOL  
HEAT  
PARK  
PARK  
LINE  
CIRCULATOR  
BLOWER  
XFMR  
EAC  
HUM  
PARK  
INDUCER  
IGNITOR  
IND  
IGN  
IGN N  
IND N  
HUMIDIFIER  
ELECTRONIC  
AIR CLEANER  
Y
W
G
R
Y
W
G
R
COMPRESSOR  
CONTACTOR  
24 V  
HUMIDIFIER  
THERMOSTAT  
C
(E2)  
24 V HUM  
FLAME  
SENSOR  
PROBE  
(E33)  
FP  
PRESSURE SWITCH (N. O.)  
PSI  
PSO  
HLI  
HLO  
HIGH LIMIT  
AUX. HIGH  
LIMIT (N. C.)  
RO OUT  
GND  
(N. C.)  
ROLLOUT  
(N. C.)  
RO IN  
2 STAGE  
GAS  
VALVE  
MV LO  
MV HI  
MV COM  
TR  
TH  
[12-Pin Connector]  
LEGEND  
PSO  
HLI  
PSI  
HLO  
Low Voltage (24 VAC)  
Line Voltage (120 VAC)  
MV  
LO  
RO  
RO  
GND  
OUT  
OUT  
MV  
IND  
IGN  
N
TR  
MV  
IND  
TH  
IGN  
COM  
N
N. C. = Normally closed switch  
N. O. = Normally open switch  
4-Pin Connector  
12-Pin Connector  
4
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WIRING  
TYPICAL SYSTEM WIRING TABLE  
50A66  
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)  
Terminal  
block with  
captive  
screws  
(2nd wire from Y terminal goes to 24 VAC HOT side of  
compressor contactor coil)  
C
24 VAC COMMON side of compressor contactor coil  
high limit OUTPUT  
HLO (Pin 1)  
Not Used (Pin 2)  
TH (Pin 3)  
24 VAC transformer (low voltage HIGH side)  
Not Used (Pin 4)  
RO1 (Pin 5)  
TR (Pin 6)  
PSO  
HLI  
PSI  
HLO  
rollout switch OUTPUT  
MV  
LO  
RO  
RO  
GND  
OUT  
OUT  
24 VAC transformer (low voltage COMMON side)  
high limit INPUT  
MV  
TR  
MV  
HLI (Pin 7)  
TH  
COM  
GND (Pin 8)  
MV COM (Pin 9)  
PSI (Pin 10)  
RO2 (Pin 11)  
MV (Pin 12)  
MUST BE RELIABLY GROUNDED TO CHASSIS  
gas valve COMMON  
pressure switch INPUT  
rollout switch INPUT  
gas valve  
IND  
IGN  
inducer HOT side  
ignitor HOT side  
IND  
N
IGN  
N
IND  
IGN  
IND N  
IGN N  
inducer NEUTRAL side  
ignitor NEUTRAL side  
COOL 1/4” spade terminal  
HEAT 1/4” spade terminal  
PARK (3 terminals) 1/4” spade terminal  
LINE 1/4” 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  
XFMR 1/4” spade terminal  
EAC (optional) 1/4” spade terminal  
HUM (optional) 1/4” spade terminal  
humidifier HOT side  
Terminals for 120 Volt NEUTRAL for line, transformer,  
circulator, electronic air cleaner and humidifier  
120 VOLT NEUTRAL  
1/4” spade terminal  
(5 terminals)  
3/16” spade terminal  
flame sensor probe*  
FP (E33)  
1/4” spade terminal  
FAN  
Circulator blower fan speed terminal  
24 VAC humidifier  
1/4” receptacle  
24 V HUM (E2)  
* maximum recommended flame probe wire length is 36 inches.  
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OPERATION  
OPTION SWITCHES  
The option switches on the 50A66-743 control are used  
to determine the length of the heat delay-to-fan-off period.  
The following table shows the time periods that will result  
from the various switch positions.  
satisfied, the gas valve is de-energized. After proof of  
flameloss, theinducerblowerremainsenergizedtopurge  
the system for 5 seconds and the delay-to-fan-off period  
begins. When the purge is complete, the inducer blower  
andhumidifierarede-energized.Afterthedelay-to-fan-off  
period ends, the circulator fan and electronic air cleaner  
are de-energized.  
OPTION SWITCH POSITIONS  
If flame is not detected, both valves are de-energized,  
the ignitor is turned off, and the 50A66 control goes into  
the “retry” sequence. The “retry” sequence provides a  
15-secondwaitfollowinganunsuccessfulignitionattempt  
(flame not detected).After this wait, the ignition sequence  
is restarted. If this ignition attempt is unsuccessful, three  
more retries will be made before the control goes into  
system lockout.  
HEAT delay-  
to-fan-off:  
Set switch  
#1  
#2  
60 sec.  
90 sec.*  
120 sec.  
180 sec.  
Off  
Off  
On  
On  
Off  
On  
Off  
On  
COOL delay-  
to-fan-off:  
Set switch  
#3  
Ifameisdetected,thenlost,the50A66controlwillrepeat  
the initial ignition sequence for a total of three “recycles”.  
After three unsuccessful “recycle” attempts, the control  
will go into system lockout.  
2 sec.  
45 sec.*  
Off  
On  
* Factory Setting  
If flame is established for more than 10 seconds after  
ignition, the50A66controllerwillcleartheignitionattempt  
(or retry) counter. If flame is lost after 10 seconds, it will  
restart the ignition sequence.This can occur a maximum  
of four times before system lockout.  
HEAT MODE  
In a typical system, a call for heat is initiated by closing  
the thermostat contacts. This starts the 50A66 control’s  
heating sequence.The inducer blower and humidifier are  
energized. After a 15-second prepurge period, the 768A  
Silicon Nitride ignitor is powered.  
A momentary loss of gas supply, ame blowout, or a  
shorted or open condition in the flame probe circuit will be  
sensed within 2 seconds. The gas valve will de-energize  
andthecontrolwillrestarttheignitionsequence.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.  
This controller 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 the control  
goes into retry mode. For the second attempt to ignite  
gas within the same call for heat, the control increases  
the ignitor 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.  
Ifthecontrolhasgoneintosystemlockout,itmaybepossi-  
ble to reset the control by a momentary power interruption  
of ten seconds or longer. Refer to PRECAUTIONARY,  
SYSTEM LOCKOUT, AND DIAGNOSTIC FEATURES.  
COOL MODE  
In a typical system, a call for cool is initiated by closing  
the thermostat contacts. This starts the 50A66 control’s  
cooling sequence. The compressor is energized and the  
delay-to-fan-on period begins. After the delay-to-fan-on  
period ends, the circulator fan is energized at cool speed.  
Theelectronicaircleaner(optional)isalsoenergized.After  
thethermostatissatisfied,thecompressorisde-energized  
and the delay-to-fan-off period begins. After the delay-to-  
fan-off period ends, the circulator fan and electronic air  
cleaner are de-energized.  
The 80 VAC Silicon Nitride ignitor manufactured by  
White-Rodgersmustbeused.Theseignitorsarespecial-  
ly designed to operate with the 50A66’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.  
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.  
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 and  
the humidifier are energized. When the thermostat is  
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SYSTEM LOCKOUT AND DIAGNOSTIC FEATURES  
2. Interrupt the 24 VAC power at the control for at least  
SYSTEM LOCKOUT FEATURES  
ten seconds. You may also need to reset the flame  
rollout sensor switch.  
Whensystemlockoutoccurs,thegasvalveisde-energized.  
The circulator blower may be energized at heat speed for  
some faults, 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.)  
3. Afteronehourinlockout,thecontrolwillautomatically  
reset itself.  
DIAGNOSTIC FEATURES  
To reset the control after system lockout, do one of  
The 50A66-743 control continuously monitors its own  
operation and the operation of the system. If a failure oc-  
curs, the DS 1 (red) and DS 2 (green) LEDs will indicate  
a failure code as shown below.  
the following:  
1. Interrupt the call for heat at the thermostat for at least  
one second, but for less than 20 seconds (if flame is  
sensedwiththegasvalvede-energized,interruptingthe  
call for heat at the thermostat will not reset the control).  
7
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TROUBLESHOOTING  
DIAGNOSTIC TABLE  
DS 1 (Red) DS 2 (Green) Error/Condition  
Comments/Troubleshooting  
Simultaneous Simultaneous  
slow flash slow flash  
Normal operation  
No fault  
Simultaneous Simultaneous  
Normal operation with Normal operation  
call for heat  
fast flash  
Slow flash  
Off  
fast flash  
On  
Open limit switch  
Verify continuity through rollout switch circuit  
Slow flash  
Pressure switch stuck  
closed/open  
Pressure switch stuck closed. Check switch function, verify  
inducer is turning off.  
Pressure switch stuck open. Check pressure switch function  
and tubing. Verify inducer is turning on and pulling sufficient  
vacuum to engage switch.  
Alternate  
slow flash  
Alternate slow  
flash  
External lockout  
(retries)  
Failure to sense flame is often caused by carbon deposits on  
the flame sensor, a disconnected or shorted flame sensor  
lead or a poorly grounded furnace. Carbon deposits can be  
cleaned with emery cloth. Verify sensor is not contacting the  
burner and is located in a good position to sense flame.  
Ignitor must be positioned to light the gas immediately when  
the valve opens. If the ignitor has been replaced, verify hot  
spot position has not changed.  
Check sensor lead for shorting and verify furnace is  
grounded properly.  
Slow flash  
Off  
Flame sensed with gas Verify the gas is operating and shutting down properly. Flame  
valve de-energized  
in burner assembly should extinguish promptly at the end of  
the cycle. Check orifices and gas pressure.  
On  
On  
Slow flash  
Open rollout switch  
Verify continuity through rollout switch circuit.  
On  
Module – internal fault Module contacts for gas valve not operating or processor  
condition  
fault. Reset control, if condition persists, replace module.  
Slow flash  
Fast flash  
Low flame sense  
current  
Low flame sense current is often caused by carbon deposits  
on the flame sensor, a poorly grounded furnace or a mis-  
aligned flame sense probe. Carbon deposits can be cleaned  
with emery cloth.  
Check or improve furnace and module ground. Verify sensor  
is located in or very near flame as specified by the appliance  
manufacturer.  
Fast flash  
Slow flash  
Grounding or  
reversed polarity  
Verify the control and furnace are properly grounded. Check  
and reverse polarity (primary) if incorrect.  
Alternate fast  
flash  
Alternate fast  
flash  
Module ignitor  
contact failure  
Fault code indicates the module ignitor contacts are not  
functioning properly. Replace module.  
HOMEOWNER HELP LINE: 1-800-284-2925  
White-Rodgers is a business  
of Emerson Electric Co.  
The Emerson logo is a  
trademark and service mark  
of Emerson Electric Co.  

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