Two Stage 50M61-495 Sequence Of Operation - American Standard 50A65-475 Manual

Two Stage 50M61-495 Sequence of Operation

White-Rodgers Integrated Furnace Control
50M61-495 Models
When the service disconnect 1 is in the "ON" position,
power is applied through the blower door interlock
switch 6 to the controls line voltage input terminals 8
and out of the control to the primary side of the
control transformer "XFMR" u. The secondary side
of the control transformer supplies 24 volts to the
control through terminal "TH" and "TR" po. Control
terminal "R" ; 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 z
on the control. The control checks and confirms
normally closed contacts at the temperature cut
out"TCO" j, auxiliary limit (downflow and
some upflow/horizontal models), the flame roll-out
bi-metal control (two bi-metal controls are now used
on downflow/horizontal models) l and normally open
contacts at the safety pressure switch #1 j. With all
safety and control switches in their proper position,
the control will energize the induced draft motor on
high speed w and flash the LED two times per second
continuously (fast flash) during a call for heat.
When safety pressure switch "#1" j closes, the
control switches the induced draft motor to low speed w
and begins the ignition sequence. The hot surface
|ignitor w is energized for several seconds (see note)
allowing the thermal element to heat up. The control
then switches 24 volts to its "MVL" and "MV COM" g
terminals to terminals #1 g and #2 f 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" ; 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 flamed current is not
sensed by the control within the trial for ignition period
(see note), the main valve low and redundant gas
valve solenoids ga are de-energized. The control
will begin an interpurge cycle and adds additional
seconds to the hot surface ignitor warm-up timing
(see note). 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 (see note), the control will
repeat the previous cycle before locking out. At the
end of the indoor blower motor delay "ON" timing, line
voltage is applied at control terminal "HEAT LO" 6
energizing the indoor blower motor at low heat
fan speed, 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 thermostat terminal "W2" to
the "W2" terminal z on the control. A 30 second,
2nd stage recognition time delay begins. At the end of
the 30 second delay, the induced draft motor is
switched to high speed w causing pressure switch #2 d
to close. When pressure switch #2 closes, 24 volts are
switched from control terminal "MVH" d to the gas
valve terminal #3 d energizing the second stage
solenoid allowing increased gas flow to the
burners. At the same time, the indoor blower motor
is switched to high heat fan speed 7.
When second stage thermostat contacts "W2" satisfy,
the induced draft motor is switched back to low speed w
causing pressure switch #2 d to open, breaking the
circuit to the second stage gas valve solenoid d. Gas
flow is reduced to the burners. The indoor blower
motor will switch back to low heat fan speed after a
30 second delay 6.
When first stage thermostat contacts "W1" satisfy,
the main valve low and the redundant gas valve
solenoids g are de-energized extinguishing main
burner flame. Once the control senses the loss of
flame current (0.7 sec.) ;, the induced draft motor w
is de-energized after a five second post-purge 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.
Note: See Timing Chart for details or the Integrated Furnace
Control Label.
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