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Two Stage V/S Vent and V/S Blower Motor Models
Sequence of Operation
First Stage Heat
When the integrated furnace control, IFC, receives a call
for first stage heat on "W1" the following will occur:
1.
The IFC microcomputer runs a self-check routine.
2.
The IFC checks the high limit switches, TCO-A,
TCO-B, and the flame roll-out switch.
3.
The IFC checks the variable speed vent motor
RPM/SOA circuit for the proper "OFF" state signal
(SOA = Safe Operating Area).
4.
The IFC calls the variable speed vent motor for
low speed operation on IND.LOW pin #4 circuit.
5.
The variable speed vent motor ramps up in speed
until it sees the low pressure switch, PS1, LPS/PS1,
close. The variable speed vent motor reports this
to the IFC on the RPM/SOA circuit.
6.
Ignitor warm-up period begins. 20 seconds maxi-
mum time.
7.
The gas valve is energized on low.
8.
Trial for ignition period begins within four seconds.
9.
Prove flame within two seconds.
10. Cycle off ignitor and start time count for the indoor
blower.
11. Reset flame failure time to 0.7 seconds.
12. 45 seconds after flame is proved start the indoor
blower.
Second Stage Heat
When the IFC control receives a call for second stage
heat on "W2" and flame is present, the control will
wait 30 seconds before sending a signal to the variable
speed vent motor and the indoor blower for high
speed operation.
1.
The variable speed vent motor ramps up in speed
until is sees the high pressure switch, HPS/PS2,
close. Then the variable speed vent motor reports
this to the IFC on the RPM/SOA circuit.
2.
When the IFC sees the high speed vent motor
signal, it energizes the gas valve on high.
Second Stage Satisfied, First Stage Still Calling
1.
The IFC will remove the high speed signal to the
variable speed vent motor and the indoor blower;
the motors go to low speed operation.
2.
The IFC de-energizes the high fire gas valve.
First Stage Satisfied
1.
The IFC turns off the gas valve.
2.
When the IFC sees no flame current, no flame, it
starts the five second postpurge cycle and then
turns off the variable speed vent motor.
3.
The cool down cycle is started by the IFC. The cool
down time can be changed; the factory setting is
100 seconds.
Call For First and Second Stage Together
There will be a 10 minute delay after low fire is estab-
lished before the IFC will allow high fire operation.
30
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