440 01 2021 01
44
11. Sequence of Operation & Diagnostics (*9MPV)
The following is the normal operating sequence.
Cooling (Y) Request:
24VAC signals applied to Y & G terminals of FCB (furnace control board).
(Must have Y & G for cooling)
·
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.
Cooling (Y) and dehumidification (DEHUM) requests:
·
24 VAC signals applied to Y, DEHUM & G terminals of FCB (furnace control board).
·
Same operation as the cooling (Y) request, except the cooling speed is reduced 20% to compensate for high
humidity conditions during cooling operation. The cooling speed returns to the normal setting after the DEHUM signal is removed.
Continuous Circulating Fan (G) Request:
24VAC signal applied to G terminal of FCB.
·
Continuous fan speed is energized.
G signal removed from FCB.
·
Continuous fan speed is de--energized without delay.
NOTE 1) Blower motor runs at the continuous fan speed selected by DIP Switches 1 & 2 in response to a G request.
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.
NOTE 3) Hard--wire option not available for variable speed models.
Heating (W1) Request (single stage thermostat operation, 3
rd
DIP switch (SW1- 3) on the FCB
must be in off position) (see furnace wiring diagram):
24VAC signal applied to W1 terminal of FCB.
·
Inducer motor turns on at high speed and pressure switches close.
·
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 blower 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 for the Heat Fan Off Delay time to expire, the FCB will wait for the
selected Heat Fan Off Delay, and then start a new heating cycle.
Heating (W1 & W2) Request (two stage thermostat operation, 3
rd
DIP (SW1- 3) switch must be in
on position) (see furnace wiring diagram):
24VAC signals applied to W1 terminal of FCB.
·
Same response as single stage thermostat operation described above except the burners, inducer, and blower 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 burners light at high heat rate, the inducer
remains on high speed after ignition, and the FCB will delay High Heat blower operation for the 30--second High Stage Heat Fan
On Delay.
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
Page 48: ...440 01 2021 01 48 ...
