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heat airflow for 90, 120, 150, or 180 seconds (depending
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 Fig. 35 and 36 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 thermostat
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- -energized to close the NC contact.
When sufficient pressure is available the high- -heat pres-
sure 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 thermostat
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 pres-
sure 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 suffi-
ciently, 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 Fig. 35 and 36 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 Fig. 58. The electronic air cleaner
terminal EAC- -1 is energized with 115 vac when the
blower motor BLWM is operating.
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 continue operating at
cooling airflow for an additional 90 seconds. Jumper Y/Y2
to DHUM to reduce the cooling off- -delay to 5 seconds.
See Fig. 35.
b. Single- -Stage Thermostat and Two- -Speed Cooling
(Adaptive Mode) - -
See Fig. 35 and 36 for thermostat connections.
This furnace can operate a two- -speed cooling unit with a
single- -stage thermostat because the furnace control CPU
includes a programmed adaptive sequence of controlled
operation, which selects low- -cooling or high- -cooling
operation. This selection is based upon the stored history
of the length of previous cooling period of the single- -stage
thermostat.
NOTE: The air conditioning relay disable jumper ACRDJ must
be connected to enable the adaptive cooling mode in response to a
call for cooling. See Fig. 35. When ACRDJ is in place the furnace
control CPU can turn on the air conditioning relay ACR to
energize the Y/Y2 terminal and switch the outdoor unit to
high- -cooling.
The furnace control CPU can start up the cooling unit in either
low- - or high- -cooling. If starting up in low- -cooling, the furnace
control CPU determines the low- -cooling on- -time (from 0 to 20
minutes) which is permitted before switching to high- -cooling. If
the power is interrupted, the stored history is erased and the furnace
control CPU will select low- -cooling for up to 20 minutes and then
energize the air conditioning relay ACR to energize the Y/Y2
terminal and switch the outdoor unit to high- -cooling, as long as
the thermostat continues to call for cooling. Subsequent selection is
based on stored history of the thermostat cycle times.
The
wall
thermostat
“calls
for
cooling”,
closing
the
R- -to- -G- -and- -Y circuits. The R- -to- -Y1 circuit starts the outdoor
unit on low- -cooling speed, and the R- -to- -G- -and- -Y1 circuits starts
the furnace blower motor BLWM at low- -cooling airflow which is
the true on- -board CF selection as shown in Fig. 58.
If the furnace control CPU switches from low- -cooling to
high- -cooling, the furnace control CPU will energize the air
conditioning relay ACR. When the air conditioning relay ACR is
energized the R- -to- -Y1- -and- -Y2 circuits switch the outdoor unit to
high- -cooling speed, and the R- -to- -G- -and- -Y1- -and- -Y/Y2 circuits
transition the furnace blower motor BLWM to high- -cooling
airflow. High- -cooling airflow is based on the A/C selection shown
in Fig. 35.
NOTE: When transitioning from low- -cooling to high- -cooling the
outdoor unit compressor will shut down for 1 minute while the
furnace blower motor BLWM transitions to run at high- -cooling
airflow.
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- -Y circuit 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 Fig. 35.
c. Two- -Stage Thermostat and Two- -Speed Cooling
See Fig. 35 and 36 for thermostat connections
NOTE: The air conditioning relay disable jumper ACRDJ must
be disconnected to allow thermostat control of the outdoor unit
staging. See Fig. 35.
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
true on- -board CF (continuous fan) selection as shown in Fig. 59.
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 Fig. 58.
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
Fig. 35.
Page 86
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