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54
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. 57.
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
selectionshowninFig.57.
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. 26.)
c. Two--Stage Thermostat and Two--Speed Cooling
See Fig. 33 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. 26.)
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. 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 (air conditioning)
selectionshowninFig.57.
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. 26.)
4. Thermidistat Mode
See Fig. 27--29 for thermostat connections.
The dehumidification output, DHUM on the Thermidistat
should be connected to the furnace control thermostat ter-
minal 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 ap-
plies to operation with a Thermidistat. The exceptions are
listed below:
a. Low cooling-- W h e n t h e R -- t o -- G -- a n d -- Y 1 c i r c u i t i s
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 (continuous fan) selection as
shown in Fig. 55.
b. High cooling-- W h e n t h e R -- t o -- G -- a n d Y / Y 2 c i r c u i t i s
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 (air conditioning)
selectionshowninFig.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 fur-
nace control is in the Thermidistat mode and there is a de-
mand for dehumidification. The cooling operation de-
scribed 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 dehumidi-
fication is satisfied. Low--cooling airflow is the true
on--board CF (continuous fan) selection as shown in
Fig. 57.
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 dehumidi-
fication is satisfied. High--cooling airflow is based on
the A/C (air conditioning) selection shown in Fig. 57.
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 (continuous fan) selection shown in Fig.
57. Factory default is shown in Fig. 57. Terminal EAC--1
is energized as long as the blower motor BLWM is ener-
gized.
During a call for heat, the furnace control CPU will trans-
ition the blower motor BLWM to continuous blower air-
flow, low--heat airflow, or the mid--range airflow,
whichever is lowest. The blower motor BLWM will re-
main ON until the main burners ignite then shut OFF and
remain OFF for the blower--ON delay (45 seconds in low--
heat, and 25 seconds in high--heat), allowing the furnace
heat exchangers to heat up more quickly, then restarts at
the end of the blower--ON delay period at low--heat or
high--heat airflow, respectively.
The blower motor BLWM will revert to continuous--
315AAV