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2. Two- -Stage Thermostat and Two- -Stage Heating
Fig. 38 and 39 for thermostat connections)
NOTE: In this mode the LHT 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
switch to HI HEAT speed five sec after the R- -to- -W2 cir-
cuit 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 switch to LO HEAT speed five sec after
the R- -to- -W2 circuit opens.
3. Cooling Mode- -The thermostat "calls for cooling."
a. Single- -Speed Cooling- -
See Fig. 38 and 39 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 COOL speed.
The electronic air cleaner terminal 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 on the
COOL speed for an additional 90 sec. Jumper Y/Y2 to
DHUM to reduce the cooling off- -delay to 5 sec. See Fig.
38.
b. Single- -Stage Thermostat and Two- -Speed Cooling
(Adaptive Mode)
See Fig. 38 and 39 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. 38. When ACRDJ is in place, the furnace
control CPU can turn on the air conditioning relay ACR to
See
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- -cool speed (same speed as LO HEAT).
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
switch the furnace blower motor BLWM to COOL speed.
NOTE: When transitioning from low- -cooling to high- -cooling the
outdoor unit compressor will shut down for 1 minute while the
BLWM continues to run at low- -cool speed (same speed as
LO- -HEAT) until the outdoor unit compressor comes back on at
high speed.
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 sec. Jumper Y1 to DHUM to reduce the cooling off- -delay to 5
sec. See Fig. 38.
c. Two- -Stage Thermostat and Two- -Speed Cooling See
Fig. 38 and 39 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. 38.
The
thermostat
closes
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- -cool speed (same speed as
LO HEAT). 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 on COOL speed. 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 sec. Jumper Y1 to DHUM to reduce
the cooling off- -delay to 5 sec. See Fig. 38.
4. Dehumidification Mode
See Fig. 38 and 39 for Thermidistat connections.
The dehumidification output, D or DHUM on the Ther-
midistat should be connected to the furnace control thermo-
stat terminal DHUM. The dehumidification output, D or
DHUM from a thermostat. When there is a dehumidify de-
mand, 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 in-
put is turned ON when no dehumidify demand exists. Once
24 vac is detected by the furnace control on the DHUM in-
put, the furnace control dehumidification capability is acti-
vated. If the DHUM input is low for more than 48 hours,
the furnace control reverts back to non- -Thermidistat mode.
81
the
R- -to- -G- -and- -Y1
circuits
for
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