Bryant 926TC Installation, Start-Up, Operating And Service And Maintenance Instructions page 72

926TC: Installation, Start-up, Operating and Service and Maintenance Instructions
g. Switching from High- to Low-Heat -The furnace control CPU
will not switch from high-heat to low-heat while the thermostat
R-to-W circuit is closed when using a single-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. The inducer motor IDM will remain
energized for a 15-second post-purge period, after which the
inducer motor IDM will stop, the low-heat pressure switch LPS
will open de-energizing the humidifier terminal HUM. 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 the
HEAT-OFF delay selection). The furnace control CPU is
factory-set for a 120-second Heat-OFF delay.
2. Two-Stage Thermostat and Two-Stage Heating
See Fig. 39 for thermostat connections.
NOTE: In this mode (Htt) must be set to (2St) 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 (Htt).
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 energized
to close the NO contact. When sufficient pressure is available the
high-heat pressure switch HPS closes, and the high-heat gas
valve solenoid 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 pressure switch relay HPSR is
de-energized to open the NO contact and de-energize the
high-heat gas valve solenoid GV-HI. When the inducer motor
IDM reduces pressure sufficiently, 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 seconds after the R-to-W2 circuit opens.
3. Cooling mode
The thermostat "calls for cooling".
a. Single-Speed Cooling-
See Fig. 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 high cooling airflow.
High cooling airflow is based on the high cooling speed (CL2)
selection. 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 circuits are
opened. The outdoor unit will stop, and the furnace blower motor
BLWM will continue operating at cooling airflow for an
additional (See Fig. 59) 5, 30, or 90 seconds (depending on the
cooling blower-OFF delay (Cod) setting). The furnace CPU is
factory set for a 90 second cooling blower-OFF delay.
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
b. Single-Stage Thermostat and Two-Speed Cooling (Adaptive
Mode) -
See Fig. 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 operation.
This selection is based upon the stored history of the length of
previous cooling period of the single-stage thermostat.
NOTE: (Ctt) must be set to (1St) to enable the adaptive cooling mode
in response to a call for cooling. See
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. Low cooling airflow is based on the low
cooling blower speed (CL1) selection. See
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
high-cooling blower speed (CL2) selection.
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 5, 30, or
90 seconds (depending on the cooling blower-OFF delay (Cod) setting).
The furnace CPU is factory set for a 90 second cooling blower-OFF
delay (See Fig. 59).
c. Two-Stage Thermostat and Two-Speed Cooling
See Fig. 39 for thermostat connections
NOTE: (Ctt) setting must be set to (2st) to allow thermostat control
of the outdoor unit staging. (See
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 based on low cooling blower speed (CL1) selection.
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 high
cooling blower speed (CL2) selection. (See
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 5, 30, or 90 seconds (depending on the cooling
blower-OFF delay (Cod) setting). The furnace CPU is factory set for a
90 second cooling blower-OFF delay (See
4. Dehumidification Mode
See Fig. 39 for thermostat connections.
The dehumidification output on the thermostat should be connected
72
Fig. 59. When (Ctt) is set to (1St)
Fig. 59.
Fig. 59).
Fig. 59)
Fig. 59).