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12. Sequence of Operation & Diagnostics (*9MPT)
The following is the normal operating sequence.
Cooling (Y) 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.
NOTE: DEHUM not available on the *9MPT modesl.
Continuous Circulating Fan (G) Request:
24VAC signal applied to G terminal of FCB.
·
Low--Heat motor speed is energized without delay.
G signal removed from FCB.
·
Low--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 follow-
ing 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 (W1) Request (single stage thermostat operation, 3
rd
DIP switch (SW1- 3) must be in off
position) (see furnace wiring diagram):
24VAC signal applied to W1 terminal of FCB.
·
Inducer motor turns on at high speed.
·
Following a 15 second prepurge delay after the low pressure switch closes, the ignitor begins a 17 second warm up.
·
The gas valve is energized, the main burners light at low heat rate and flame is sensed.
·
The ignitor is de--energized, and the inducer drops to low speed after the main burners ignite.
·
The FCB will delay Low Heat blower operation for the 45--second Low Heat Fan On Delay time, timed from
the opening of the gas valve.
·
If the W1 request is still present after 12 minutes, timed from the opening of the gas valve, the inducer switches to high speed,
closing the high pressure switch, then the high fire solenoid energizes, and the fan switches to High Heat speed.
W1 signal removed from FCB.
·
The gas valve de--energizes and the main burners go out.
·
The inducer runs at its present speed for a 15 second postpurge period.
·
The fan runs at its present speed.
·
The fan de--energizes after the selected Heat Fan Off Delay time expires, timed from the gas valve de--energizing.
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.
Heating Request (W1 & W2) (two stage thermostat operation, 3
rd
DIP switch (SW1- 3) must be in
on position) (see furnace wiring diagram):
24VAC signal applied to W1 terminal of FCB.
·
Same response as single stage thermostat operation (fan uses Low Stage Heat On Delay) described above except the control
will not go to high heat rate, and High Heat Fan speed unless a W2 signal is applied.
24VAC signal applied to W1 and W2 terminals of FCB.
·
Same light--off routine as described for the signal stage thermostat operation except main burners light at high heat rate, the
inducer remains on high speed after ignition, and the FCB will delay blower operation at the High Heat Fan speed for 30 second
On Delay time.
NOTE 5) The FCB responds without delay to the presence or loss of W2 (with W1 constant). W1 & W2 result in high inducer, high heat
rate, and High Heat Fan speed. W1 only results in low inducer, low heat rate, and Low Heat Fan speed.
Summary of Contents for *9MPT050F12
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