Carrier PG96VAT Manual page 86

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. 39 and 40 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 sole-
noid 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 sufficient-
ly, 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 sec-
onds after the R−to−W2 circuit opens.
3. Cooling mode
The thermostat "calls for cooling".
a. Single−Speed Cooling−
See Fig. 39 and 40 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. 66. The electronic air cleaner
terminal EAC−1 is energized with 115 vac when the blow-
er motor BLWM is operating.
When the thermostat is satisfied, the R−to−G−and−Y cir-
cuits are opened. The outdoor unit will stop, and the fur-
nace blower motor BLWM will continue operating at cool-
ing airflow for an additional 90 seconds. Jumper Y/Y2 to
DHUM to reduce the cooling off−delay to 5 seconds. See
Fig. 39.
b. Single−Stage Thermostat and Two−Speed Cooling
(Adaptive Mode) −
See Fig. 39 and 40 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 op-
eration. 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. 39. 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
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. 66.
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. 39.
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. 39.
c. Two−Stage Thermostat and Two−Speed Cooling
See Fig. 39 and 40 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. 39.
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. 67.
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. 66.
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. 39.
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for cooling", closing the