Sequence Of Operation; Adaptive Heating Mode - Bryant 330AAV Installation, Start-Up, And Operating Instructions Manual

2-stage thermostat to select gas heating modes. The W2 from
thermostat must be connected to W2 on control terminal block.
(See Fig. 10.)
CAUTION: This furnace is equipped with a manual
reset limit switch in the gas control area. The switch will
open and shut off power to the gas valve if a flame rollout
or overheating condition occurs in the gas control area.
DO NOT bypass the switch. Correct inadequate
combustion-air supply, component failure, or restricted
flue gas passageway before resetting the switch.
Before operating furnace, check each manual reset switch for
continuity. If necessary, press and release button to reset switch.
B. Sequence of Operation
Using schematic diagram in Fig. 13, follow the sequence of
operation through the different modes. Read and follow diagram
very carefully.
NOTE: If power interruption occurs during "call for heat" (W/W1
or W/W1 and W2) and if the thermostat is still calling for gas
heating, the control will start a 90-sec blower only on period 2 sec
after power is restored. The red LED will flash code 12 during
90-sec period, after which the LED will be on continuously as long
as no faults are detected. After 90-sec period, furnace will respond
to the thermostat normally.
The blower door must be installed for power to be conducted
through blower door interlock switch ILK to furnace control CPU,
transformer TRAN, inducer motor IDM, blower motor BLWM,
hot surface ignitor HSI, and gas valve GV.
1. Adaptive Heating Mode—Single-Stage Thermostat with
2-Stage Heating
(See Fig. 9 for thermostat connections.)
NOTE: With high-heat-only switch SW-1 off, low-heat-only
switch SW-2 selects either the low-heat-only operation mode when
on (see item 2 below), or adaptive heating mode when off in
response to a call for heat. (See Fig. 11.) When high-heat-only
switch (SW-1) is in ON position, it always causes high-gas-heat
operation when R-W/W1 circuit is closed, regardless of setting of
low-heat-only switch (SW-2).
EAC - ELECTRONIC
AIR CLEANER
(115-VAC 1 AMP MAX)
7 8 9
4 5 6
1 2 3
Fig. 11—Control Center
3-AMP
FUSE
LED -
DIAGNOSTIC
LIGHT
10 11 12
7 8 9
4 5 6
TWIN / TEST
1 2 3
TERMINAL
MASTER SLAVE
1
HUM -
HUMIDIFIER
(24-VAC 0.5
AMP MAX)
24-VOLT
THERMOSTAT
TERMINALS
FURNACE AND
BLOWER OFF DELAY
SETUP SWITCHES
A93348
—11—
This furnace can operate as a 2-stage furnace with a
single-stage thermostat because furnace control CPU in-
cludes a programmed adaptive sequence of controlled
operation, which selects low-gas-heat or high-gas-heat op-
eration. This selection is based upon the stored history of
the length of previous gas heating on/off periods of the
single-stage thermostat.
The furnace will start up in either low- or high-gas heat. If
the furnace starts up in low-gas heat, the control CPU
determines the low-gas heat on time (from 0 to 16 minutes)
which is permitted before switching to high-gas heat.
If power is interrupted, the stored history is erased. When
this happens, the control CPU selects low-gas heat for up to
16 minutes and then switches to high-gas heat, as long as
the thermostat continues to call for heat. Subsequent selec-
tion is based on stored history of thermostat cycle times.
When wall thermostat "calls for heat", R-W/W1 circuit
closes. The furnace control performs a self check, verifies
the low-heat and high-heat pressure switch contacts LPS
and HPS are open, and starts inducer motor IDM in low
speed or high speed as appropriate.
a. Inducer prepurge period—As inducer motor IDM comes
up to low speed or high speed, the low-heat pressure
switch contacts LPS (or LPS and HPS) close to begin a
15 sec prepurge period.
b. Ignitor warm-up—At end of prepurge period, the hot
surface ignitor HSI is energized for a 17-sec ignitor
warm-up period.
c. Trial-for-ignition sequence—When ignitor warm-up pe-
riod is completed, the main gas valve relay contacts
MGVR-1 and -2 close to energize the low-heat gas valve
solenoid GV. The gas valve opens, and 24-v power is
supplied for a field-installed humidifier at terminals
HUM and C . The low-heat gas valve solenoid GV
OM
permits gas flow to the burners where it is ignited. After
5 sec, the ignitor HSI is de-energized, and a 2-sec
flame-proving period begins.
If high-heat gas valve solenoid GV is also energized
after normally closed high-heat pressure switch relay
HPSR closes and after inducer motor IDM goes to high
speed and provides sufficient pressure to close high-heat
pressure switch HPS. HPSR is open while furnace is
powered in standby mode. If high-heat pressure switch
HPS fails to close and low-heat pressure switch LPS
closes, furnace operates at low-heat gas flow rate until
high-heat pressure switch closes.
d. Flame-proving—When burner flame is proved at flame-
proving sensor electrode FSE, the control CPU begins
blower on delay period and continues to hold gas valve
GV open. If burner flame is not proved within 2 sec, the
control CPU closes gas valve GV, and the control CPU
repeats the ignition sequence for up to 3 more trials-for-
ignition before going to ignition lockout. LOCKOUT IS
RESET AUTOMATICALLY after 3 hr, or by momen-
tarily interrupting 115-v power to furnace, or by inter-
rupting 24-v power at SEC1 or SEC2 to the control CPU
(not at W/W1, G, R, etc.). Opening thermostat R-W
circuit will not reset an ignition lockout.
If flame is proved when flame should not be present, the
control CPU locks out of gas heating mode and operates
inducer motor IDM on high speed until flame is no
longer proved.
e. Blower on delay—If burner flame is proven, 45 sec after
gas valve GV is opened the blower motor BLWM is
energized on the appropriate heating speed, low-gas-heat