White Rodgers Thermostat 50A55 438 User Manual

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, 264” 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, 464” 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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