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high- -heat airflow five seconds after the furnace control
CPU switches from low- -heat to high- -heat.
g. Switching from High- - to Low- -Heat - -The furnace con-
trol CPU will not switch from high- -heat to low- -heat while
the thermostat R- -to- -W circuit is closed when using a sin-
gle- -stage thermostat.
h. Blower- -Off Delay - -When the thermostat is satisfied, the
R to W circuit is opened, de- -energizing the gas valve GV- -
M, stopping gas flow to the burners, and de- -energizing the
humidifier terminal HUM. The inducer motor IDM will re-
main energized for a 15- -second post- -purge period. The
blower motor BLWM and air cleaner terminal EAC- -1 will
remain energized at low- -heat airflow or transition to low- -
heat airflow for 90, 120, 150, or 180 seconds (depending
on selection at blower- -OFF delay switches). The furnace
control CPU is factory- -set for a 120- -second blower- -OFF
delay.
2. Two- -Stage Thermostat and Two- -Stage Heating
See Fig. 39 and 40 for thermostat connections.
NOTE: In this mode the low- -heat only switch SW1- -2 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
transition to high- -heat airflow five seconds after the
R- -to- -W2 circuit 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 transition to low- -heat airflow five sec-
onds after the R- -to- -W2 circuit opens.
3. Cooling mode
The thermostat "calls for cooling".
a. Single- -Speed Cooling- -
See Fig. 39 and 40 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. 64. The electronic air cleaner
terminal EAC- -1 is energized with 115 vac when the blow-
er 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-
440 01 4800 01
nace blower motor BLWM will continue operating at cool-
ing airflow for an additional 90 seconds. Jumper Y/Y2 to
DHUM to reduce the cooling off- -delay to 5 seconds. See
Fig. 39.
b. Two- -Stage Thermostat and Two- -Speed
Cooling
See Fig. 39 and 40 for thermostat connections
The
thermostat
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
CF
(continuous
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) selection shown in Fig. 64.
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.
4. Dehumidfy Mode
See Fig. 39 and 40 for thermostat connections.
The H output on the humidify sensing thermostat 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
Deactivation
Once 24 vac is detected by the furnace control on the
DHUM input, the furnace control operates in dehumidify
mode. If the DHUM input is low for more than 48 hours,
the furnace control reverts back to non- -dehumidify mode.
The cooling operation described in Item 3, Cooling mode.
above also applies to operation with a humidity sensing
thermostat. 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 low cool-
ing airflow demand is reduced by 10 percent.
b. High cooling- -When the R- -to- -G- -and Y/Y2 circuit is
closed and there is a demand for dehumidification, high
cooling airflow demand is reduced by 10 percent.
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 sec-
onds.
5. Continuous Blower Mode
When the R- -to- -G circuit is closed by the thermostat, the
blower motor BLWM will operate at continuous blower air-
flow. Continuous blower airflow selection is initially based
on the CF (continuous fan) selection shown in Fig. 64. Fac-
tory default is shown in Fig. 64. Terminal EAC- -1 is ener-
gized as long as the blower motor BLWM is energized.
During a call for heat, the furnace control CPU will transi-
tion the blower motor BLWM to continuous blower airflow
or low- -heat airflow whichever is lowest. The blower motor
BLWM will remain 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), allow-
ing 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- -blower
airflow after the heating cycle is completed. In high- -heat,
Specifications subject to change without notice.
closes
the
R- -to- -G- -and- -Y1
fan)
selection
as
shown
no
dehumidify
demand
circuits
for
in
64.
The
Activation/
exists.
79
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