Single Stage 50A65-474 Sequence Of Operation - American Standard 50A65-475 Manual

Single Stage 50A65-474 Sequence of Operation

White-Rodgers Integrated Furnace
Controls 50A65-474 with Silicon Nitride
Hot Surface Ignitor (SiNi HSI) – Part No.
CNT02854, Superseded to CNT03076
When the disconnect 1 is in the "ON" position, power
is applied through the blower door interlock switch 6
to the control line voltage input terminal 8 and out of
the control to the primary side of the control
transformer "XFMR" e. The low voltage side of the
transformer supplies 24 volts to the control through
terminals "TH" o and "TR" i. Control terminal "R" ;
supplies 24 volts to the "R" terminal of the room
thermostat.
Once power is applied, the control flashes the LED
"ON" for one second and performs a self check
routine. Following the normal system check, the
control flashes the LED light once per second
continuously (slow flash) while in stand-by.
On a call for heat, 24 volts are applied from the room
thermostat's terminal "W" to the "W" terminal ; on
the control. The control checks and confirms normally
closed contacts at the temperature cut out "TCO" f, or
the fuse link auxiliary limit (downflow and some
upflow/horizontal models) j, the flame roll-out switch
j and normally open contacts of the safety pressure
switch "PS" f. With all safety and control switches in
their proper position, the control will energize the
induced draft motor y and flash the LED light two
times per second continuously (fast flash) during a
call for heat.
When the safety pressure switch "PS" f closes, the
control begins the ignition sequence. The SiNi hot
surface ignitor y is energized for several seconds
(see page 11) allowing the thermal element to heat
up. The control then switches on 24 volts to the gas
valve "MV" terminal #1 a. The redundant and main
solenoids are energized allowing gas flow and main
burner ignition. When flame current is detected by
the control through its terminal "FP" k, the 45 second
indoor blower motor delay on timing 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 control k within
four seconds, the trial for ignition period, the redundant
and main gas valve solenoids a are de-energized.
The control will begin an interpurge cycle and may
add additional AC sine wave cycles to the hot
surface ignitor warm-up cycle (see SiNi HSI write up).
The control energizes the gas valve a for the second
attempt to establish main burner ignition. If flame
current is not sensed by the control on the second
retry within the trial for ignition period, the control
will repeat the previous cycle one additional time
before locking out.
At the end of the indoor blower delay on time, line
voltage is applied at the controls terminal "HEAT" 5
energizing the indoor blower motor at heating fan
speed, supplying warm air to the space.
When the thermostat is satisfied, the valve's redundant
and main solenoids a are de-energized, extinguishing
main burner flame. Once the control senses loss of
flame current (0.7 sec.) k, the induced draft motor t
is de-energized after a five second post-purge cycle.
The indoor blower motor delay off timing begins. At
the completion of the fan delay off timing, the
indoor blower motor 5 is de-energized and the cycle
is complete.
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