GF - A 20
Furnace Sequences Of Operation
*UH3 Sequence of Operation
· The communicating comfort control (17) signals the furnace
IFC for first stage heat. (16)
· The IFC then checks all safeties, thermostats
(10) & pressure switches PS-1, 2 & 3. (9)
· The IFC signals the variable speed inducer drive (8) to start
the vent motor (8) and go to its second stage speed.
· The IFC then signals the variable speed inducer motor drive
board (8) to ramp down the vent motor in steps to the first
stage vent motor speed. The reduction of the vent motor speed
in steps allows the gas flow through the gas valve to also be
reduced in steps.
· When the IFC no longer detects the 24 Volt AC signal from
pressure switch # 2, PS-2, (9) it will signal the indoor blower
(4) to go to its first stage heating speed.
· The communicating comfort control (16) will continue to call
for first stage heat operation until the indoor temperature is
back at the communicating comfort control set point OR,
· If the communicating comfort control (17) does not detect
that the indoor temperature is moving back towards its set point
or the indoor temperature is still moving away from the
communicating comfort control set point, it will signal the IFC
(16) to go to second stage heat.
· The IFC (8) signals the variable speed inducer drive (8)
to ramp the vent motor up in steps to its learned second
stage RPM speed.
· As the vent motor (8) speed increases the amount of gas
coming through the gas valve will increase.
· When the IFC detects a 24 Volt AC signal that pressure
switch #2, PS-2, (9) is closed, the IFC will then signal the
indoor blower (4) to go to its second stage heat speed.
· The communicating comfort control (17) will continue to call
for second stage heat operation until the indoor temperature
approaches its set point. Before the indoor temperature reaches
the communicating comfort control (17) set point the
communicating comfort control will signal the furnace IFC to
go back to first stage operation OR,
· If the communicating comfort control (17) senses the indoor
temperature is not moving back towards its set point or the
indoor temperature is still moving away from the communicating
comfort control set point, it will signal the furnace IFC to go
to third stage heat.
· The IFC signals the variable speed inducer drive board (8)
to ramp the vent motor in steps to its learned third stage RPM
speed.
· As the vent motor speed increases the amount of gas coming
through the gas valve will increase.
· When the IFC detects a 24 Volt AC Signal from Pressure
Switch #3, PS-3, (9) closing, the IFC will then signal the
indoor blower (4) to go to its third stage heat speed.
NOTE:
The numbers in parentheses refer to the numbers along
the left side of the diagram 1.
NOTE:
The furnace lights in Second Stage mode.
· First & second stage pressure switches PS-1 & 2 close.
(9)
· The IFC receives a 24 Volt AC signal from pressure switches
PS-1 & PS-2 when they close. (9) This verifies the vent
motor is moving the correct amount of combustion air
through the furnace and vent system.
· IFC starts the hot surface igniter learning routine warm
up time cycle. (6)
· IFC turns on the gas valve. (11) Trial time for ignition is
five seconds.
· The IFC verifies ignition by the flame current sensing
method. (7) If a flame is not detected, the IFC will cycle the
furnace three times to try and verify a flame. If no flame is
detected, the IFC will lock out for one hour. The IFC will send an
alert code to the communicating comfort control and user
interface. The IFC will also flash its Red alert LED two
times repeatedly.
· If a flame is detected, the IFC will start the heat exchanger
warm-up time delay for the indoor blower.
· After 45 seconds, the IFC signals the indoor blower (4)
to engage and run at its second stage heat speed.
2
3
4e4c 4d4b4a
5a 5b 5c
6a
6b
5a 5b
3
5a
5b
6b
7
8
3
9
2
1 11
10
3
10
6a 6b
8
5b
10
2
2
3
6a
6b
6b
8
5b
3
10
2
2
3
6a
6b
6b
5c
10
UH3 Sequence of Operation
3
3
3
3
3
3
3
3
2
3
3
3
To Next Page
Loading...
