Bryant 312AAV - Manual (Page 17)

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.
NOTE: In this mode the low-heat-only switch 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.
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 pressure switch HPS closes, and the high-heat gas
valve solenoid GV-HI is energized. The blower motor
BLWM will switch to HI-HEAT speed 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 energized to open the NC
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 ener-
gized as long as the low-heat pressure switch LPS
remains closed. The blower motor BLWM will switch to
LO-HEAT speed five seconds after the R-to-W2 circuit
opens.
3. Cooling Mode
The thermostat “calls for cooling.”
a. Single-Speed Cooling- (See Fig. 21 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 operat-
ing.
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 on
the COOL speed for an additional 90 seconds. Jumper
Y/Y2 to DHUM to reduce the cooling off-delay to 5
seconds. (See Fig. 22.)
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. 22.) 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.
b. Single-Stage Thermostat and Two-Speed Cooling
(Adaptive Mode)-(See Fig. 31 for thermostat connec-
tions)
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 periods of the single-
stage thermostat.
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 initially 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.
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 termi-
nal 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. 22.)
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 continues to run at low-cool speed
(same speed as LO-HEAT) until the outdoor unit compressor
comes back on at high speed.
c. Two-Stage Thermostat and Two-Speed Cooling-(See
Fig. 30 for thermostat connections)
TABLE 8-SETUP SWITCH DESCRIPTION
SETUP
SWITCH NO.
NORMAL
POSITION
DESCRIPTION
OF USE
SW-1
Low-Gas Heat (Adaptive Mode)
OFF (Single-Stage Thermostat)
Turn switch off for installations with single-stage thermo-
stats; control selects low-gas-heat or high-gas-heat opera-
tion based on previous cycles. Turn switch on for installa-
tions with 2–stage thermostats to permit only low-gas-heat
operation in response to closing R-W/W1. High-gas heat is
supplied only when R-to-W/W1-and-W2 are closed.
SW-2 and SW3 ON, OFF
Switches control gas heating mode blower off delay. (See
Table B).
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