48
441 01 2121 01
and continues to hold the gas valve GV−M open. If
the burner flame is not proved within two seconds,
the control CPU will close the gas valve GV−M, and
the control CPU will repeat the ignition sequence for
up to three more Trials−For−Ignition before going to
Ignition−Lockout. Lockout will be reset automatically
after three hours, or by momentarily interrupting 115
vac power to the furnace, or by interrupting 24 vac
power at SEC1 or SEC2 to the furnace control CPU
(not at W/W1, G, R, etc.). If flame is proved when
flame should not be present, the furnace control
CPU will lock out of Gas−Heating mode and oper-
ate the inducer motor IDM on high speed until flame
is no longer proved.
e. Blower−On delay − If the burner flame is proven
the blower−ON delays for low−heat and high−heat
are as follows:
Low−heat − 45 seconds after the gas valve GV−M
is opened the blower motor BLWM is turned ON at
low−heat airflow.
High−heat − 25 seconds after the gas valve GV−M
is opened the BLWM is turned ON at high−heat
airflow. Simultaneously, the humidifier terminal HUM
and electronic air cleaner terminal EAC−1 are ener-
gized and remain energized throughout the heating
cycle.
f. Switching from Low− to High−Heat − If the fur-
nace control CPU switches from low−heat to high−
heat, the furnace control CPU will switch the in-
ducer motor IDM speed from low to high. The
high−heat pressure switch relay HPSR is de−ener-
gized to close the NC contact. When sufficient pres-
sure is available the high−heat pressure switch
HPS closes, and the high−heat gas valve solenoid
GV−HI is energized. The blower motor BLWM will
transition to high−heat airflow five seconds after the
furnace control CPU switches from low−heat to
high−heat.
g. Switching from High− to Low−Heat
−The furnace
control CPU will not switch from high−heat to low−
heat while the thermostat R−to−W circuit is closed
when using a single−stage thermostat.
h. Blower−Off Delay −When the thermostat is satis-
fied, the R to W circuit is opened, de−energizing the
gas valve GV−M, stopping gas flow to the burners,
and de−energizing the humidifier terminal HUM.
The inducer motor IDM will remain energized for a
5−second post−purge period. The blower motor
BLWM and air cleaner terminal EAC−1 will remain
energized at low−heat airflow or transition to low−
heat airflow for 90, 120, 150, or 180 seconds (de-
pending on selection at blower−OFF delay
switches). The furnace control CPU is factory−set
for a 120−second blower−OFF delay.
2. Two−Stage Thermostat and Two−Stage Heating
See Figure 27−Figure 33 for thermostat connections.
NOTE: In this mode the low−heat only switch SW1−2 must
be ON to select the low−heat only operation mode in
response to closing the thermostat R−to−W1 circuit. Closing
the thermostat R−to− W1−and−W2 circuits always causes
high−heat operation, regardless of the setting of the low−heat
only switch.
The wall thermostat “calls for heat”, closing the R−to−W1
circuit for low−heat or closing the R
−to−W1−and−W2 circuits
for high−heat. The furnace control performs 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
high−speed.
The start up and shut down functions and delays described in
item 1. above apply to the 2−stage heating mode as well,
except for switching from low− to high−Heat and vice versa.
a. Switching from Low− to High−Heat − If the ther-
mostat R−to−W1 circuit is closed and the R−to−W2
circuit closes, the furnace control CPU will switch
the inducer motor IDM speed from low to high. The
high−heat pressure switch relay HPSR is de−ener-
gized to close the NC contact. When sufficient pres-
sure is available the high−heat pressure switch
HPS closes, and the high−heat gas valve solenoid
GV−HI is energized. The blower motor BLWM will
transition to high−heat airflow five seconds after the
R−to−W2 circuit closes.
b. Switching from High− to Low−Heat −If the ther-
mostat R−to− W2 circuit opens, and the R−to−W1
circuit remains closed, the furnace control CPU will
switch the inducer motor IDM speed from high to
low. The high−heat pressure switch relay HPSR is
energized to open the NC contact and de−energize
the high−heat gas valve solenoid GV−
HI. When the
inducer motor IDM reduces pressure sufficiently, the
high−heat pressure switch HPS will open. The gas
valve solenoid GV−M will remain energized as long
as the low−heat pressure switch LPS remains
closed. The blower motor BLWM will transition to
low−heat airflow five seconds after the R−to−W2
circuit opens.
3. Cooling mode
The thermostat “calls for cooling”.
a. Single−Speed Cooling−
See Figure 27 for thermostat connections
The thermostat closes the R−to−G−and−Y circuits.
The R−to− Y circuit starts the outdoor unit, and the
R−to−G−and−Y/Y2 circuits start the furnace blower
motor BLWM on cooling airflow. Cooling airflow is
based on the A/C selection shown in Figure 55. The
electronic air cleaner terminal EAC−1 is energized
with 115 vac when the blower motor BLWM is oper-
ating.
When the thermostat is satisfied, the R−to−
G−and−Y circuits are opened. The outdoor unit will
stop, and the furnace blower motor BLWM will con-
tinue operating at cooling airflow for an additional
90 seconds. Jumper Y/Y2 to DHUM to reduce the
cooling off−delay to 5 seconds. (See Figure 26)
b. Two−Stage Thermostat and Two−Speed Cooling
See Figure 28 for thermostat connections
The thermostat closes the R−to−G−and−Y1 circuits for
low−cooling or closes the R−to−G−and−Y1−and−Y2 circuits
for high−cooling. The R−
to−Y1 circuit starts the outdoor unit
on low−cooling speed, and the R−to−G−and−Y1 circuit starts
the furnace blower motor BLWM at low−cooling airflow which
is the CF (continuous fan) selection as shown in Figure 53.
The R−to−Y1−and−Y2 circuits start the outdoor unit on
high−cooling speed, and the R−to− G−and−Y/Y2 circuits start
the furnace blower motor BLWM at high−cooling airflow.
High−cooling airflow is based on the A/C (air conditioning)
selection shown in Figure 55.
The electronic air cleaner terminal EAC−1 is energized with
115 vac whenever the blower motor BLWM is operating.
When the thermostat is satisfied, the R−to−G−and−Y1 or
R−to− G−and−Y1−and−Y2 circuits are opened. The outdoor
unit stops, and the furnace blower BLWM and electronic air
cleaner terminal EAC−1 will remain energized for an
additional 90 seconds. Jumper Y1 to DHUM to reduce the
cooling off−delay to 5 seconds. (See Figure 26)
4. Dehumidfy Mode
See Figure 27−Figure 33 for thermostat connections.
The H output on the humidify sensing thermostat
should be connected to the furnace control thermostat
terminal DHUM. When there is a dehumidify demand,
the DHUM input is activated, which means 24 vac sig-
nal is removed from the DHUM input terminal. In other
words, the DHUM input logic is reversed. The DHUM
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