d. Flame-proving—When the burner flame is proved at the
flame-proving sensor electrode FSE, the control CPU
begins the blower on delay period and continues to hold the
gas valve GV open. If the burner flame is not proved within
2 sec, the control CPU closes the gas valve GV, and the
control CPU repeats the ignition sequence for up to 3 more
trials-for-ignition before going to ignition lockout. LOCK-
OUT IS RESET AUTOMATICALLY after 3 hrs, or by
momentarily interrupting 115-v power to the furnace, or by
interrupting 24-v power at SEC1 or SEC2 to the control
CPU (not at W/W1, G, R, etc.). Opening the thermostat
R-W circuit will not reset an ignition lockout.
If flame is proved when flame should not be present, the
control CPU locks out of gas heating mode and operates
the inducer motor IDM on high speed until flame is no
longer proved.
e. Blower on delay—If the burner flame is proven, 45 sec
after the gas valve GV is opened the blower motor BLWM
is energized on the appropriate heating speed, low-gas-heat
or high-gas-heat speed. Simultaneously, the EAC terminals
EAC-1 and EAC-2 are energized with 115v and remain
energized as long as the blower motor BLWM is energized.
f. Switching from low- to high-gas heat—If the furnace
control CPU switches from low-gas heat to high-gas heat,
the control CPU switches the inducer motor IDM speed
from low to high. The high-heat pressure switch relay
HPSR closes. When the inducer motor IDM provides
sufficient pressure to close the high-heat pressure switch
HPS, the high-heat gas valve solenoid GV is energized. The
blower motor BLWM switches speed for high-gas heat 5
sec after the control CPU switches from low-gas heat to
high-gas heat.
g. Switching from high- to low-gas heat—The control CPU
will not switch from high-gas heat to low-gas heat while
the thermostat R-W circuit is closed when a single-stage
thermostat is used.
h. Blower off delay—When the thermostat is satisfied, the
R-W circuit is opened, de-energizing the gas valve GV,
stopping gas flow to the burners, and de-energizing the
humidifier terminals HUM and Com. The inducer motor
IDM remains energized for a 5-sec post-purge period. The
blower motor BLWM and EAC terminals EAC-1 and
EAC-2 remain energized for 90, 135, 180, or 225 sec
(depending on selection at blower off delay switches SW-3
and SW-4). The furnace control CPU is factory set for a
135-sec blower off delay.
2. Non-Adaptive Heating Mode—Two-Stage Thermostat and
2-Stage Heating
(See Fig. 13 for thermostat connections.)
NOTE:
The low-heat-only switch SW-2 on selects the low-heat-
only operation mode in response to closing the thermostat
R-W/W1 circuit. When the high-heat-only switch SW-1 is off,
closing the thermostat R to W1-and-W2 circuits is required for
high-gas-heat operation. When the high-heat-only switch SW-1 is
on, it always causes high-gas-heat operation when the R-W/W1
circuit is closed, regardless of the setting of the low-heat-only
switch SW-2 and regardless of whether the R-W2 circuit is closed
or open.
The start-up and shutdown functions and delays described in
item 1. above apply to the 2-stage heating mode as well,
except for switching from low- to high-gas heat and vice
versa.
a. When the wall thermostat "calls for heat," the R-W/W1
circuit closes for low-gas heat or the R to W1-and-W2
circuits close for high-gas heat. The furnace control per-
forms a self-check, verifies the low-heat and high-heat
pressure switch contacts LPS and HPS are open, and starts
the inducer motor IDM in low speed or high speed as
appropriate.
b. Switching from low- to high-gas heat—If the thermostat
R-W/W1 circuit for low-gas heat is closed and the R-W2
circuit for high-gas heat closes, the control CPU switches
the inducer motor IDM speed from low to high. The
high-heat pressure switch relay HPSR closes. When the
inducer motor IDM provides sufficient pressure to close
the high-heat pressure switch HPS, the high-heat gas valve
solenoid GV is energized. The blower motor BLWM
switches speed for high-gas heat 5 sec after the R-W2
circuit closes.
c. Switching from high- to low-gas heat—If the thermostat
R-W2 circuit for high-gas heat opens and the R-W/W1
circuit for low-gas heat remains closed, the control CPU
switches the inducer motor IDM speed from high to low.
The high-heat pressure switch relay HPSR opens to de-
energize the high-heat gas valve solenoid GV. When the
inducer motor IDM reduces pressure sufficiently, the
high-heat pressure switch HPS opens. The low-heat gas
valve solenoid GV remains energized as long as the
low-heat pressure switch LPS remains closed. The blower
motor BLWM switches speed for low-gas heat 5 sec after
the R-W2 circuit opens.
3. Cooling Mode
a. Single-Speed Cooling Outdoor Unit
(See Fig. 12 for thermostat connections.)
(1.) The thermostat closes the R to G-and-Y circuits. The
R-Y circuit starts the outdoor unit, and the R to
G-and-Y circuits start the furnace blower motor
BLWM on high-cool speed.
(2.) The EAC terminals EAC-1 and EAC-2 are energized
with 115v when the blower motor BLWM is operat-
ing.
(3.) When the thermostat is satisfied, the R to G-and-Y
circuits are opened. The outdoor unit stops, and the
furnace blower motor BLWM continues operating on
the high-cool speed for an additional 90 sec.
b. Two-Speed Cooling Outdoor Unit
(See Fig. 13 for thermostat connections.)
(1.) The thermostat closes the R to G-and-Y1 circuits for
low cooling or closes the R to G-and-Y1-and-Y/Y2
circuits for high cooling. The R-Y1 circuits start the
outdoor unit on low-cooling speed, and the R-G circuit
starts the furnace blower motor BLWM on low-
cooling speed (same speed as for low-gas heat). The R
to Y1-and-Y2 circuits start the outdoor unit on high-
cooling speed, and the R to G-and-Y2 circuits start
the furnace blower motor BLWM on high-cooling
speed.
NOTE:
Y1 is not located on the furnace control, but is found in
the outdoor unit. The furnace control CPU controls blower motor
BLWM speed by sensing only G for low-cooling speed and Y/Y2
for high-cooling speed.
(2.) The EAC terminals EAC-1 and EAC-2 are energized
with 115v when the blower motor BLWM is operating
on either cooling speed.
12