38
DHUM to reduce the cooling off--delay to 5 seconds. (See
Fig. 33.)
2.
Single--Stage Thermostat and Two--Speed Cooling
(Adaptive Mode)
(See Fig. 50 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. 33.) 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. 39.
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. 33.)
3.
Two--Stage Thermostat and Two--Speed Cooling
(See Fig. 49 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. 33.)
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 on low--cooling
airflow which is the true on--board CF selection as shown
in Fig. 41. 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 ariflow. High--cooling airflow is based on
the A/C selection shown in Fig. 39.
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. 33.)
THERMIDISTAT MODE
See Fig. 43--46 for Thermidistat 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 applies to
operation with a Thermidistat. The exceptions are listed below:
1.
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%
of low--cooling airflow which is the true on--board CF
selection as shown in Fig. 39.
2.
High coolin
g--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% of high--cooling airflow. High--cooling airflow is
based on the A/C selection shown in Fig. 39.
3.
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.
SUPER--DEHUMIDIFY MODE
Super--Dehumidify mode can only be entered if the furnace
control is in 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:
1.
Low cooling
--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% 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. 39.
58U
VB
