Two Stage 50A61 Sequence Of Operation - American Standard 50A65-475 Manual

Two Stage 50A61 Sequence Of Operation

White-Rodgers Integrated Furnace Control
50A61-605 Model – Part No. CNT02536
When the service disconnect 1 is in the "ON" position,
power is applied through the blower door interlock
switch 3 to the controls line voltage input terminal t
and out of the control to the primary side of the control
transformer "XFMR" 0. The secondary side of the
control transformer supplies 24 volts to the control
through terminals "TH" and "TR" f. Control terminal
"R" l supplies 24 volts to the "R" terminal of the room
thermostat.
Once power is applied, the control flashes the LED light
"ON" for one second and performs a self check routine.
Following the normal system check, the control flashes
the LED one time per second (slow flash) continuously
while in stand-by.
On a call for heat, 24 volts are applied from the room
thermostat's "W1" terminal to the "W1" terminal l on
the IFC control. The IFC control checks and confirms
normally closed contacts at the temperature cut out
"TCO" i, the auxiliary limit (downflow and some
upflow/horizontal models) p, the flame roll-out switch
p, and checks the variable speed vent motor RPM/SOA
4 and 0 circuit for the proper "OFF" state signal (SOA
= Safe Operating Area). With all safety and control
switches in their proper position, the IFC control will
call the variable speed vent motor for low speed
operation 4 on the low speed line IND.LO Plug E10 pin
#4 q and flash the RED LED 9 two times per second
continuously (fast flash) during a call for heat.
When the safety pressure switch LPS/PSI u closes, the
variable speed vent motor reports this to the IFC on the
RPM/SOA circuit 4 and 0. The SiNi hot surface ignitor
q is energized for several seconds allowing the thermal
element to heat up. The control then switches 24 volts
to its "MVL" d terminal and pin #1 on the gas valve.
The redundant and main solenoids are energized
allowing gas flow and main burner ignition. When
flame current is sensed by the control through its "FP"
a terminal, the 45 second indoor blower motor time
delay "ON" begins. Flame failure response time is set
for two seconds. After flame has been established for
ten seconds, the flame failure response time is reset for
0.7 seconds. If flame current is not sensed by the IFC
control within the trial for ignition period, the main
valve low and redundant gas valve solenoids d are de-
energized. The control will begin an interpurge cycle
and add additional AC sine wave cycles to the hot
surface ignitor warm-up timing cycle (see SiNi HSI
write up). The control energizes the gas valve for the
second attempt to establish main burner ignition.
If again flame current is not sensed by the control
within the trial for ignition period, the control will
repeat the previous cycle before locking out. The
control will automatically reset in one hour. At the end
of the indoor blower motor delay "ON" timing, the IFC
control will apply 24 volts A.C. to Plug P1 pin #2 and 7
volts D.C. to pin #15. Pin #15 is the input command to
the variable speed motor to turn on and pin #2 is the
input command line to run at the low heat airflow,
supplying warm air to the space.
If the temperature in the space continues to fall, the
thermostat second stage contacts "W2" close. 24 volts
are switched from the thermostat terminal "W2" to the
"W2" terminal l on the IFC control. A 30 second, 2nd
stage recognition time delay begins. At the end of the
30 second delay, the IFC control will call the variable
speed vent motor for high speed operation q Plug E10
pin #5. The IFC switches 24V to the gas valve terminal
#3 s energizing the second stage solenoid, allowing
increased gas flow to the burners. At the same time the
IFC control calls, the indoor blower motor for high heat
fan speed y switches operation by applying 24 volts
AC to Plug P1 pin #13, which is "W2" CFM.
When second stage thermostat contacts "W2" satisfy,
the IFC will remove the high speed call from the
variable speed vent motor IND.HI pin #5 q. The
pressure switch HPS/PS2 t opens and the variable
speed vent motor reports this to the IFC control on the
RPM/SOA circuit 4 and 0. The IFC control will turn off
the 24 volts to the gas valve MVH pin #3 s. Gas flow is
reduced to the burners. The indoor blower motor will
be switched back to low heat fan speed after a 30
second delay.
When first stage thermostat contacts "W1" satisfy, the
main valve low and the redundant gas valve solenoids
are de-energized extinguishing main burner flame.
Once the control senses the loss of flame current (0.7
sec.), the variable speed vent motor 2 is de-energized
after a five second postpurge cycle. The indoor blower
motor "OFF" timing begins. At the end of the indoor
blower motor "OFF" timing, the indoor blower motor is
de-energized and the cycle is complete.
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