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high-heat. Thefurnace c ontrol performs a self-check, and
verifies the low-heat and medium-heat
pressure
switch c ontacts
LPS and MPS are open, then de-energizes
the HPSR relay t o
close the NCcontact.
The start upand shut down f unctions and delays described
above
apply t othe 2-stage medium/high
heating mode a s well, e xcept
forswitching from high- t omedium-heat.
1.Switching from High-
to Medium-Heat
--
If the ther-
mostat R to W2 circuit opens,
and the R to Wl
circuit re-
mains closed,
the furnace
control
CPU will gradually
de-
crease
the
inducer
motor
speed
to
the
required
medium-heat
RPM.
When
the inducer
motor
IDM
re-
duces pressure
sufficiently,
the high
heat pressure
switch
HPS will open
and the high-heat
gas valve solenoid
GV-
HI will be de-energized.
The gas valve
solenoid
GV-M
will remain
energized
as long
as the low-heat
pressure
switch LPS remains
closed.
When the inducer
motor speed
gets within
15% of the required
medium-heat
RPM
the
furnace
control
CPU will start a 5 second
blower
airflow
change
delay. After the 5 second
blower
airflow
change
delay
is completed
the blower
airflow
will transition
to
medium-heat
airflow.
Cooling
Mode
The thermostat
"calls for cooling."
2. Single-Speed
Cooling
See Fig. 29 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. 47.
The electronic
air cleaner
ternfinal
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
cir-
cuits are opened.
The outdoor
unit will stop, and the fur-
nace
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. 33.)
3. Single-Stage
Thermostat
and Two-Speed
Cooling
(Ad-
aptive Mode)
See Fig. 59 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
nmst
be connected
to enable
the adaptive
cooling
mode in response
to
a call for cooling.
(See
Fig.
33.) When
in place
the furnace
control
CPU
can turn
on the
air conditioning
relay
ACR
to
energize
the
Y/Y2
ternfinal
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 deternfines
the low-cooling
on-time
(from 0 to 20
nfinutes)
which is pernfitted
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 nfinutes
and then energize
the air conditioning
relay ACR to energize
the
Y/Y2
ternfinal
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
5O
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. 47.
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 Yl-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. 47.
NOTE:
When transitioning from low-cooling
to high-cooling
the outdoor unit compressor will shut down for 1 nfinute while
the furnace
blower
motor
BLWM
transitions
to
run
at
high-cooling
airflow.
The electronic air cleaner ternfinal 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 ternfinal 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. 33.)
4. Two-Stage Thermostat and Two-Speed Cooling
See Fig. 58 for thermostat connections.
NOTE:
The air conditioning relay disable jumper ACRDJ nmst
be disconnected to allow thermostat control of the outdoor unit
staging. (See Fig. 33.)
The thermostat closes the R to G-and-Y1
circuits for low cooling
or closes the R to G-and-Yl-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. 47. The R to Yl-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. 47.
The electronic air cleaner ternfinal 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-Yl-and-Y2
circuits are opened. The outdoor unit stops,
and the furnace blower BLWM and electronic air cleaner ternfinal
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. 33.)
Thermidistat
Mode
See Fig. 52-55 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 Thernfidistat
mode. If the DHUM input is low for more than 48 hours, the
furnace control reverts back to non-Thernfidistat
mode.
The cooling operation described above also applies to operation
with a Thernfidistat. The exceptions are listed below:
1. Low cooling - When the R to G-and-Yl
circuit is closed
and there is a demand for dehunfidification,
the furnace
blower motor BLWM will drop the blower airflow to 86%
of low cooling airflow which is the true on-board CF se-
lection as shown in Fig. 47.
2. High cooling - When the R to G-and Y/Y2 circuit is
closed and there is a demand for dehunfidification,
the fur-
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