Carrier 58CVA Installation, Start-Up, Operating And Service And Maintenance Instructions page 45

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. 32.) When 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. 55.
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 55.
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. 32.)
c. Two-Stage Thermostat and Two-Speed Cooling
See Fig. 31 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. 32.)
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 selection as
shown in Fig. 55. 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 selection shown in Fig. 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
Fig. 32.
4. Thermidistat Mode
See Fig. 24-27 for thermostat connections
The dehumidification output, DHUM on the Thermidistat
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 signal is removed from
the DHUM input terminal. In other words, the DHUM input
logic is reversed. The DHUM input is turned ON when no
dehumidify demand exists. Once 24 vac is detected by the
furnace control on the DHUM input, the furnace control
operates in Thermidistat mode. If the DHUM input is low for
more than 48 hours, the furnace control reverts back to
non-Thermidistat mode.
The cooling operation described in item 3. above also applies
to operation with a Thermidistat. The exceptions are listed
below:
a. Low cooling-When the R to G-and-Y1 circuit is closed and
there is a demand for dehumidification, the furnace blower
motor BLWM will drop the blower airflow to 86 percent of
low-cooling airflow which is the true on-board CF selec-
tion as shown in Fig. 55.
b. High cooling-When the R to G-and Y/Y2 circuit is closed
and there is a demand for dehumidification, the furnace
blower motor BLWM will drop the blower airflow to 86
percent of high-cooling airflow. High-cooling airflow is
based on the A/C selection shown in Fig. 55.
c. Cooling off-delay-When the "call for cooling" is satisfied
and there is a demand for dehumidification, the cooling
blower-off delay is decreased from 90 seconds to 5
seconds.
5. Super-Dehumidify Mode
Super-Dehumidify mode can only be entered if the furnace
control is in the Thermidistat mode and there is a demand for
dehumidification. The cooling operation described in item 3.
above also applies to operation with a Thermidistat. The
exceptions are listed below:
a. When the R to Y1 circuit is closed, R to G circuit is open,
and there is a demand for dehumidification, the furnace
blower motor BLWM will drop the blower airflow to 65
percent of low-cooling airflow for a maximum of 10
minutes each cooling cycle or until the R to G circuit closes
or the demand for dehumidification is satisfied. Low-
cooling airflow is the true on-board CF selection as shown
in Fig. 55.
b. When the R to Y/Y2 circuit is closed, R to G circuit is
open, and there is a demand for dehumidification, the
furnace blower motor BLWM will drop the blower airflow
to 65 percent of high-cooling airflow for a maximum of 10
minutes each cooling cycle or until the R to G circuit closes
or the demand for dehumidification is satisfied. High-
cooling airflow is based on the A/C selection shown in Fig.
55.
c. When the "call for cooling" is satisfied and there is a
demand for dehumidification, the cooling blower-off delay
is decreased from 90 seconds to 5 seconds.
6. Continuous Blower Mode
When the R to G circuit is closed by the thermostat, the blower
motor BLWM will operate at continuous blower airflow.
Continuous blower airflow selection is initially based on the
CF selection shown in Fig. 55. Factory default is shown in Fig.
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