50
•
The percentage of heating demand is sent from the
furnace control board to determine what RPM the
draft inducer should run at. A higher percentage
demand will drive the inducer RPM higher. This will
cause the gas valve to modulate higher. The burner
will modulate based on the inducer speed
•
Circulator blower is energized on heat speed following
a thirty (30) second blower on delay. The circulator
blower CFM will increase or decrease with gas valve
modulation. Electronic air cleaner terminal is energized
with circulator blower.
•
Furnace is now operating on the specified stage called
for by the thermostat.
•
Furnace runs, integrated control module monitors safety
circuits continuously.
•
If the two-stage thermostat changes the call from low
heat to high heat, the integrated control module will
immediately switch the induced draft blower, gas valve,
and circulator blower to their high stage settings.
•
The thermostat contacts open, completing the call for
heat.
•
Gas valve closes, extinguishing flame.
•
Induced draft blower is de-energized following a fifteen
second post purge. Humidifier contacts open.
•
Circulator blower continues running for the selected
heat off delay period (90, 120, 150 or 180 seconds).
The speed run during this period depends on the last
heat call provided by the thermostat.
If the last call for heat was a call for high heat, the air
circulating motor will run on the high heating speed for
thirty (30) seconds and then switch to the low heating
speed for the
balance
of the heat off delay period (60,
90, 120 or 150 seconds).
•
Circulator blower and electronic air cleaner terminal is
de-energized.
•
Circulator blower ramps down to OFF during the 30
seconds following the heat off delay period.
•
Furnace awaits next call from thermostat.
C
OOLING
M
ODE
The normal operational sequence in cooling mode is as fol-
lows:
•
R and Y1/G or Y2/G thermostat contacts close,
initiating a call for cool.
•
Integrated control module performs safety circuit
checks.
•
Outdoor fan and compressor are energized to their
appropriate speed.
•
Circulator blower is energized on the appropriate cool
speed at the level and time determined by the selected
ramping profile. Electronic air cleaner terminal is
energized with circulator blower.
•
Furnace circulator blower and outdoor cooling unit run their
appropriate speeds, integrated control module monitors
safety circuits continuously.
•
R and Y1/G or Y2/G thermostat contacts open,
completing the call for cool.
•
Outdoor fan and compressor are de-energized.
•
Circulator blower continues running during a cool off
delay period. The OFF delay time and airflow level are
determined by the selected ramping profile.
• Electronic air cleaner terminal and circulator blower
are de-energized.
•
Furnace awaits next call from thermostat.
F
AN
O
NLY
M
ODE
The normal operational sequence in fan only mode is as fol-
lows:
•
R and G thermostat contacts close, initiating a call for
fan.
•
Integrated control module performs safety circuit
checks.
•
Circulator blower is energized on continuous fan speed
(25%, 50%, 75% or 100% DIP switch selectable when
using a conventional thermostat). Electronic air
cleaner terminal is energized.
•
The furnace control board HUM dry contacts close.
•
Circulator blower runs, integrated control module
monitors safety circuits continuously.
•
R and G thermostat contacts open, completing the call
for fan.
•
Circulator blower is de-energized. Electronic air cleaner
terminal is de-energized.
•
Furnace awaits next call from thermostat.
O
PERATIONAL
C
HECKS
The burner flames should be inspected with the burner com-
partment door installed. Flames should be stable, quiet, soft,
and blue (dust may cause orange tips but they must not be
yellow). Flames should extend directly outward from the burn-
ers without curling, floating, or lifting off. Flames must not
impinge on the sides of the heat exchanger firing tubes.
S
AFETY
C
IRCUIT
D
ESCRIPTION
A number of safety circuits are employed to ensure safe and
proper furnace operation. These circuits serve to control any
potential safety hazards and serve as inputs in the monitoring
and diagnosis of abnormal function. These circuits are con-
tinuously monitored during furnace operation by the integrated
control module.
