Bryant 355BAV Installation, Start-Up, And Operating Instructions Manual page 39

lows:
Low- -heat- -30 seconds after the gas valve GV- -M is opened,
the BLWM is turned ON at low- -heat airflow.
High- -heat- -35 seconds after gas valve GV- -M is opened, the
BLWM is turned ON at high- -heat airflow.
Simultaneously, the humidifier terminal HUM and electron-
ic air cleaner terminal EAC- -1 are energized and remain en-
ergized throughout the heating cycle.
7. Switching From Low- - To High- - Heat- - If the furnace
control CPU switches from low- -heat to high- -heat, the fur-
nace control CPU will de- -energize the the high- -heat pres-
sure switch relay HPSR to close the NC contact and slowly
increase the inducer motor speed until the high- -heat pres-
sure switch HPS closes.
switch HPS closes, the high- -heat gas valve solenoid GV- -
HI is energized and the inducer motor RPM is noted by the
furnace control CPU. The RPM is used to evaluate vent sys-
tem resistance. This evaluation is then used to determine the
required RPM necessary to operate the inducer motor in
high- -heat mode. The blower motor BLWM will transition
to high- -heat airflow five seconds after the furnace control
CPU switches from low- -heat to high- -heat.
8. 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
single- -stage thermostat.
9. 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 hu-
midifier 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 con-
trol CPU is factory- -set for a 120- -second blower- -OFF
delay.
TWO- - STAGE THERMOSTAT AND TWO- - STAGE
HEATING
See Fig. 49 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 toW1 circuit for
low- -heat or closing the R to W1- -and- -W2 circuits for high- -heat.
The furnace control performs a self- -check and verifies the low heat
and high- -heat pressure switch contacts LPS and HPS are open.
The start- -up and shutdown functions and delays described in item
1. above apply to 2- -stage heating mode as well, except for
switching from low- - to high- -heat and vice versa.
1. 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 de- -energize the high- -heat pres-
sure switch relay HPSR to close the NC contact and slowly
increase the inducer motor speed until the high- -heat pres-
sure switch HPS closes. When the high- -heat pressure
switch closes, the high- -heat gas valve solenoid GV- -HI is
energized and the inducer motor RPM is noted by the fur-
nace control CPU. The RPM is used to evaluate vent system
resistance. This evaluation is then used to determine the re-
quired RPM necessary to operate the inducer motor in
high- -heat mode. The blower motor BLWM will transition
to high- -heat airflow five seconds after the R to W2 circuit
closes.
When the high- -heat pressure
2. 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 energize the high- -heat
pressure switch relay HPSR to open the NC contact and
slowly decrease the inducer motor speed to the required
low- -heat RPM. When the high- -heat pressure switch HPS
opens, the high- -heat gas valve solenoid GV- -HI is de- -ener-
gized. When the inducer motor IDM reduces pressure suffi-
ciently, 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.
Cooling Mode
The thermostat "calls for cooling."
1. Single- -Speed Cooling
(See Fig. 19 for thermostat connections.)
The thermostat closes R- -to- -G- -and- -Y circuits. The R- -to- -Y
circuit starts the outdoor unit, and R- -to- -G- -and- -Y/Y2 cir-
cuits start the furnace blower motor BLWM on cooling air-
flow. Cooling airflow is based on the A/C selection shown
in Fig. 39.
The electronic air cleaner terminal EAC- -1 is energized with
115- -v when 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 furnace
blower motor BLWM will continue operating at cooling air-
flow for an additional 90 sec. Jumper Y/Y2 to DHUM to
reduce the cooling off- -delay to 5 seconds. (See Fig. 33.)
2. Single- -Stage Thermostat and Two- -Speed Cooling (Ad-
aptive 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 in-
cludes a programmed adaptive sequence of controlled oper-
ation, 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
39
to high cooling airflow.