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14. Sequence of Operation & Diagnostics
The following is the normal operating sequence.
Cooling (¥) Request:
24VAC signals applied to Y & G terminals of FCB (furnace control board)
• Cool motor speed is energized after 5 second Cool Fan On Delay time.
Y & G signals removed from FCB
• Cool motor speed is de-energized after 90 second Cool Fan Off Delay time.
Continuous Circulating Fan (G) Request:
24 VAC signal is applied to G terminal of the FCB.
• Heat motor speed is energized without delay.
G signal removed from FCB.
• Heat motor speed is de-energized after 5 second delay.
NOTE 1) Furnace de-energizes the fan during the heat exchanger warm-up period on a call for Heating that occurs during a G request
unless a blower motor lead is connected to the Cont terminal on the FCB, in which case see NOTE 2).
NOTE 2) Heating or Cooling requests received during a Fan request cause the fan speed to change to the appropriate heat or cool
speed after the Fan on Delay time expires. The fan returns to continuous circulating speed after the selected Fan Off Delay time expires
following loss of the Heating or Cooling request.
Continuous Circulating Fan Hard-Wired (Cont) Request:
Field selected low speed motor tap installed on "CONT" terminal.
• Low speed is energized when power applied to furnace. Operates at this speed continuously while there are no other
blower demands from furnace control. Fan demands from furnace control for heat, cool or "G" will override hard-wired speed tap.
NOTE 3) EAC is NOT active for hard-wired mode but IS active for fan demands from furnace control for heat, cool and "G".
Heating (W) Request:
Heating (W) Request:
• 24 VAC signal applied to W terminal of FCB.
• Inducer motor turns on and the pressure switch(es) close(s).
• Following a 15 second prepurge delay after the pressure switches closes, the igniter begins a 17 second warm-up.
• The gas valve is energized, the main burners light and flame is sensed.
• The igniter is de-energized after the main burners ignite.
• FCB will delay blower operation for the 30 seconds timed from the opening of the gas valve.
W signal removed from FCB.
• The gas valve de-energizes and the main burners go out.
• The inducer runs for a 15 second postpurge period.
• The fan stays at Heat speed.
• The fan de-energizes after the selected Heat Fan Off Delay time expires, timed from the gas valve de-energizing.
HUMIDI FIE R - The 24V HUM is energized when the pressure switch closes on a call for heat. The 115V HUM (called HUM on Control)
is energized when the inducer is energized.
ELECTRONIC AIR CLEAN ER - EAC is energized when there is a blower speed call. It is NOT energized when blower operates in the
hard-wired continuous fan mode.
NOTE 4) If a new Heating request arrives while the control is waiting in the Heat Fan Off Delay time, the FCB will wait for the selected
Heat Fan Off Delay then start a new heating cycle as long as the heat call remains.
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