White Rodgers 50A55 474 Thermostat User Manual

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50A55-474 & 50A55-571  
Integrated Furnace Controls  
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 50A55-474 and 50A55-571 are automatic gas inter-  
rupted ignition controls that employ a microprocessor to  
continually monitor, analyze, and control the proper op-  
eration 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.  
9797 REAVIS ROAD  
ST. LOUIS, MISSOURI 63123-5398  
PART NO. 37-5800C  
Replaces 37-5800B  
Printed in U.S.A.  
9751  
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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:  
50A55-474 50A55-571  
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
4
0
4
TRIAL FOR IGNITION  
PERIOD  
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
2 times  
12  
1
2 times  
12  
RETRIES  
* Measured with a DC microammeter in the flame probe  
lead  
VALVE SEQUENCE  
PERIOD  
INTERPURGE  
60  
5
60  
5
OPERATING TEMPERATURE RANGE:  
-40° to 175°F (-40° to 80°C)  
POST-PURGE  
LOCKOUT TIME  
DELAY TO HEAT ON  
300  
45  
300  
45  
HUMIDITY RANGE:  
5% to 93% relative humidity (non-condensing)  
60/100/  
140/180*  
MOUNTING:  
DELAY TO HEAT OFF  
100  
Surface mount multipoise  
DELAY TO COOL ON  
DELAY TO COOL OFF  
2
2
Timing Specs: (@ 60 Hz**)  
0/80*  
0/80†  
maximum  
MINIMUM IGNITOR  
WARM-UP  
Flame Establishing Time:  
Flame Failure Response Time:  
0.8 sec  
2.0 sec  
11  
21  
17  
11  
21  
17  
MAXIMUM IGNITOR  
WARM-UP  
** At 50 Hz, all timing specifications should be increased  
by 20%.  
INITIAL IGNITOR  
WARM-UP (1st 64  
attempts)  
GasesApproved:Natural,Manufactured,Mixed,Liquified  
Petroleum, and LP Gas Air Mixtures are all approved for  
use.  
YES  
YES  
NO  
NO  
HUMIDIFIER  
ELECTRONIC AIR  
CLEANER  
* These times will vary depending on option switch  
position. The control is factory-set at 0 sec. delay  
to cool off and 100 sec. delay to heat off. See  
OPERATION section for further information.  
This time will vary depending on the condition of  
the jumper. With the jumper installed, the delay-to-  
cool-off is set at 0 seconds. To obtain an 80-  
second delay-to-cool-off, clip the jumper wire and  
separate the jumper legs.  
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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 volt-  
age. 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.  
Any orientation is acceptable.  
CAUTION  
!
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 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.  
Shut off main gas to heating system until instal-  
lation is complete.  
UL approved 105°C rated 16 gauge min., stranded, 464  
Route and secure all wiring as far from flame  
as practical to prevent fire and/or equipment  
damage.  
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.  
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.  
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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  
CIRCU-  
LATOR  
BLOWER  
XFMR  
EAC  
HUM  
IND  
IGN  
IND N  
IGN N  
INDUCER  
IGNITOR  
HUMIDIFIER  
(-474 only)  
CIR N  
LINE N  
XFMR N  
HUM N  
EAC N  
ELECTRONIC  
AIR CLEANER  
(-474 only)  
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  
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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)  
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.  
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OPERATION  
OPTION SWITCHES  
Upon a call for heat, if the warm-up time has not been  
locked, it will be decreased by one second. This reduction  
of the ignitor on-time will continue until flame fails to be  
achieved (resulting in a retry).  
(50A55-474 only)  
Theoptionswitchesonthe50A55-474controlareusedto  
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 posi-  
tions.  
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.  
OPTION SWITCH POSITIONS  
In the event of two successive retry attempts, the warm-  
up time will be unlocked and set to 21 seconds. If flame is  
then achieved, 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.  
COOL delay-  
to-fan-off:  
Set switch  
#1  
0 sec.  
80 sec.  
On  
Off  
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, thecirculatorfanisenergizedatheatspeed. Ifthere  
is an optional electronic air cleaner on the system, the  
electronicaircleanerisalsoenergized. Whenthethermo-  
stat is satisfied, the gas valve is de-energized. After proof  
of flame loss, the delay-to-fan-off period begins and the  
inducerblowerremainsenergizedtopurgethesystemfor  
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.  
COOL delay-  
to-fan-off:  
Set switch  
#2  
#3  
60 sec.  
100 sec.  
140 sec.  
180 sec.  
On  
On  
Off  
Off  
Off  
On  
On  
Off  
OPTION JUMPER  
(50A55-571 only)  
The option jumper on the 50A55-571 control is used to  
determine the length of the cool delay-to-fan-off period.  
The following table shows the time periods that will result  
from the various jumper conditions.  
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 JUMPER CONDITION  
COOL delay-  
to-fan-off:  
Jumper  
Condition  
0 sec.  
Installed  
80 sec.  
Clipped (open)  
Ifflameisdetected,thenlost,the50A55controlwillrepeat  
the initial ignition sequence for a total of ten “recycles”.  
After ten unsuccessful “recycle” attempts, 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 within one  
second.  
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 11 times before system lockout.  
These controls have an adaptive algorithm that adjusts  
the duration of the ignitor warm-up for the purpose of  
extendingignitorlife. Uponinitialapplicationofpower, 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.  
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.  
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-  
6
gize 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. Otherwise, the control will  
go into system lockout.  
DIAGNOSTIC FEATURES  
The 50A55 control continuously monitors its own opera-  
tion 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  
shownbelow. Ifthefailureisinternaltothecontrol, the  
light will stay on continuously. In this case, the entire  
control should be replaced, as the control is not field-  
repairable.IftheLEDiscontinuouslyoff,theremaybeno  
power to the control; the fuse on the control may be open;  
or there may be a failure in the control.  
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  
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-  
offperiodbegins.Aftertheoptionaldelay-to-fan-offperiod  
ends, the circulator fan and electronic air cleaner (op-  
tional) are de-energized.  
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).  
2 flashes, then pause Systemlockout(noflame)/check  
line polarity  
3 flashes, then pause Pressure switch problem  
4 flashes, then pause Thermal protection device open  
5 flashes, then pause Flame sensed with gas valve off  
6 flashes, then pause 115 Volt AC power reversed  
7 flashes, then pause Gas valve circuit error  
8 flashes, then pause Low flame sense signal  
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.  
The LED will also flash once at power-up.  
SYSTEM LOCKOUT AND  
DIAGNOSTIC FEATURES  
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.  
The diagnostic indicator light will flash or glow continu-  
ously to indicate system status. (System lockout will  
never override any precautionary features.)  
Toresetthecontrolaftersystemlockout, dooneofthe  
following:  
1. Interrupt the call for heat or cool at the thermostat for  
at least one second but less than 20 seconds (if flame  
is sensed with the gas valve de-energized, interrupt-  
ing 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. You may also need to reset the flame  
rollout sensor switch.  
3. Afteronehourinlockout,thecontrolwillautomatically  
reset itself.  
7

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