White Rodgers 50A55 285 Thermostat User Manual

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50A55-285  
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 50A55-285 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  
EMERSON ELECTRIC CO.  
9797 REAVIS ROAD  
ST. LOUIS, MISSOURI 63123-5398  
PART NO. 37-6100C  
Printed in U.S.A.  
Replaces 37-6100B  
0150  
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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:  
50A55-285  
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 WARM-UP  
(1st 64 attempts)  
17  
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  
MINIMUM IGNITOR WARM-  
UP  
5
21  
3
MAXIMUM IGNITOR WARM-  
UP  
*Measured with a DC microammeter in the flame probe lead  
IGNITION ACTIVATION  
PERIOD  
OPERATING TEMPERATURE RANGE:  
TRIAL FOR IGNITION  
PERIOD  
6
-40° to 175°F (-40° to 80°C)  
HUMIDITY RANGE:  
RETRIES  
2 times  
12  
5% to 93% relative humidity (non-condensing)  
VALVE SEQUENCE PERIOD  
INTERPURGE  
MOUNTING:  
60  
Surface mount multipoise  
POST-PURGE  
15  
Timing Specs: (@ 60 Hz**)  
maximum  
0.8 sec  
2.0 sec  
LOCKOUT TIME  
300  
30  
Flame Establishing Time:  
Flame Failure Response Time:  
HEAT DELAY-TO-FAN-ON  
HEAT DELAY-TO-FAN-OFF*  
60/90/  
120/180  
** At 50 Hz, all timing specifications should be increased by  
20%  
COOL DELAY-TO-FAN-ON  
COOL DELAY-TO-FAN-OFF  
AUTO RESET  
5
45  
Gases Approved: Natural, Manufactured, Mixed, Liquified  
Petroleum, and LP Gas Air Mixtures are all approved for use.  
60 minutes  
YES  
HUMIDIFIER  
ELECTRONIC AIR  
CLEANER  
YES  
* These times will vary depending on option switch  
position. The control is factory-set at 90 sec.  
HEAT delay-to-fan-off. See OPERATION section  
for further information.  
2
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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  
• 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.  
4
UL approved 105°C rated 16 gauge min., stranded, 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.  
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 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.  
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  
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  
RO1  
GND  
RO2  
MV  
FLAME  
SENSOR  
PROBE  
HIGH LIMIT  
(N. C.)  
AUX. HIGH  
LIMIT (N. C.)  
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  
MUST BE RELIABLY GROUNDED TO CHASSIS  
(unused terminal)  
2-pin  
connector  
& harness  
IND  
IGN  
inducer HOT side  
ignitor HOT side  
spade terminal  
spade terminal  
spade terminal  
spade terminal  
spade terminal  
spade terminal  
spade terminal  
spade terminal  
spade terminal  
spade terminal  
spade terminal  
spade terminal  
COOL  
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)  
* maximum recommended flame probe wire length is 36 inches.  
5
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OPERATION  
OPTION SWITCHES  
The option switches on the 50A55-285 control are used to  
determine the length of the heat delay-to-fan-off periods. The  
following table shows the time periods that will result from the  
various switch positions.  
Ifflameisnotdetected, bothvalvesarede-energized, theignitor  
is turned off, and the 50A55 control goes into the “retry” se-  
quence. The “retry” sequence provides a 60-second wait follow-  
ing 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.  
OPTION SWITCH POSITIONS  
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.  
HEAT delay-  
to-fan-off:  
Set switch  
#1  
#2  
60 sec.  
90 sec.*  
120 sec.  
On  
Off  
On  
Off  
On  
On  
Off  
Off  
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.  
180 sec.  
* Factory setting  
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  
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.  
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  
restarttheignitionsequence. Recycleswillbeginandtheburner  
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.  
This controller has an adaptive algorithm that adjusts the dura-  
tion 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  
onwhetherornotflameisachieved. Thewarm-uptimeislimited  
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.  
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).  
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 ener-  
gized, and the circulator fan is energized at cool speed. After the  
thermostat is satisfied, the compressor is de-energized and the  
coolmodedelay-to-fan-offperiodbegins. Afterthedelay-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 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  
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  
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 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.  
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 pe-  
riod ends, the circulator fan and electronic air cleaner are de-  
energized.  
6
DIAGNOSTIC FEATURES  
SYSTEM LOCKOUT AND  
DIAGNOSTIC FEATURES  
The 50A55 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  
Flame sensed with gas valve  
off  
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  
Continuous flashing  
(no pause)  
3. Afteronehourinlockout, thecontrolwillautomaticallyreset  
itself.  
The LED will also flash once at power-up.  
7
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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.  

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