Sequence Of Operation - Bryant 880TB Installation Instructions Manual

880TB/881TB: Installation, Start–Up, Operating and Service and Maintenance Instructions
inadequate seal may occur) and RTV sealant (G.E. 162, 6702, or
Dow-Corning 738) are needed before starting installation. DO NOT
substitute any other type of RTV sealant. G.E. 162 (P771-9003) is
available through RCD in 3-oz tubes.
12. Apply new sealant to flange of collector box and attach to cell panel
using existing screws, making sure all screws are secure.
13. Reconnect wires to the following components (Use connection
diagram on wiring label, if wires were not marked for reconnection
locations.):
a. Draft safeguard switch.
b. Inducer motor.
c. Pressure switches.
d. Limit over temperature switch.
e. Gas valve.
f. Hot surface igniter.
g. Flame-sensing electrode.
h. Flame rollout switches.
14. Reinstall internal vent pipe, if applicable.
15. Reinstall vent connector on furnace vent elbow. Securely fasten
vent connector to vent
corrosion-resistant, sheet metal screws located 180° apart.
16. Replace blower access door only if it was removed.
17. Set thermostat above room temperature and check furnace for
proper operation.
18. Verify blower airflow and speed changes between heating and
cooling.
WARNING
!
FIRE OR EXPLOSION HAZARD
Failure to follow this warning could result in personal injury, death,
and/or property damage.
Never purge a gas line into a combustion chamber. Never test for gas
leaks with an open flame. Use a commercially available soap solution
made specifically for the detection of leaks to check all connections. A
fire or explosion may result causing property damage, personal injury
or loss of life.
19. Check for gas leaks.

SEQUENCE OF OPERATION

NOTE: Furnace control must be grounded for proper operation or else
control will lock out. Control is grounded through green/yellow wire
routed to gas valve and burner box screw. Using the schematic diagram
in Fig. 47, follow the sequence of operation through the different modes.
Read and follow the wiring diagram very carefully.
NOTE: If a power interruption occurs during a call for heat (W/W1 or
W/W1-and-W2), the control will start a 90-second blower-only ON
period two seconds after power is restored, if the thermostat is still
calling for gas heating. The LED light will flash code 12 and display will
show (12.1) during the 90-sec period, after which the LED will be ON
continuous, as long as no faults are detected. After the 90-second period,
the furnace will respond to the thermostat normally.
The blower door must be installed for power to be conducted through the
blower door interlock switch ILK to the furnace control CPU,
transformer TRAN, inducer motor IDM, blower motor BLWM,
hot-surface igniter HSI, and gas valve GV.
®
1. Perfect Heat Technology - Two-Stage Heating (Adaptive
Mode) with Single-Stage Thermostat.
NOTE: See Fig. 30 for thermostat connections. Heating Thermostat
Type (Htt) can be set to either single stage (1St) or two-stage (2St) on the
control (see the Furnace Control Programming and Navigation section of
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
elbow with 2 field-supplied,
this instruction). When set to (1St), the adaptive heating mode will be
used in response to a call for heat. When the W2 thermostat terminal is
energized it will always cause high-heat operation when the R-to-W
circuit is closed, regardless of the setting of (Htt). This furnace can
operate as a two-stage furnace with a single-stage thermostat because the
furnace control CPU includes a programmed adaptive sequence of
controlled operation, which selects low-heat or high-heat operation. This
selection is based upon the stored history of the length of previous
gas-heating periods of the single-stage thermostat.
The furnace will start up in either low- or high-heat. If the furnace starts
up in low-heat, the control CPU determines the low-heat on-time (from 0
to 16 minutes) which is permitted before switching to high-heat.
If the power is interrupted, the stored history is erased and the control
CPU will select low-heat for up to 16 minutes and then switch to
high-heat, as long as the thermostat continues to call for heat.
Subsequent selection is based on stored history of the thermostat cycle
times.
The wall thermostat "calls for heat", closing the R-to-W circuit. 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.
a. Inducer Prepurge Period
(1.) If the furnace control CPU selects low-heat operation the
inducer motor IDM comes up to speed, the low-heat
pressure switch LPS closes and the furnace control CPU
begins a 15-second prepurge period. If the low-heat pressure
switch LPS fails to remain closed, the inducer motor IDM
will remain running at high-speed. After the low-heat
pressure switch re-closes, the furnace control CPU will
begin a 15-second prepurge period, and continue to run the
inducer motor IDM at high-speed.
(2.) If the furnace control CPU selects high-heat operation, the
inducer motor IDM remains running at high-speed, and 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 furnace control
CPU begins a 15-second prepurge period after the low-heat
pressure switch LPS closes. If the high-heat pressure switch
HPS fails to close and the low-heat pressure switch LPS
closes, the furnace will operate at low-heat gas flow rate
until the high-heat pressure switch closes for a maximum of
2 minutes after ignition.
b. Igniter Warm-Up -At the end of the prepurge period, the
Hot-Surface Igniter HSI is energized for a 17-second igniter
warm-up period.
c. Trial-For-Ignition Sequence -When the igniter warm-up period
is completed the main gas valve relay contact GVR closes to
energize the gas valve solenoid GV-M. Simultaneously, the 24-V
humidifier terminal HUM is energized and remains energized
while the gas valve solenoid is energized. The gas valve solenoid
GV-M permits gas flow to the burners where it is ignited by the
HSI. Five seconds after the GVR closes, a 2-second flame
proving period begins. The HSI igniter will remain energized
until the flame is sensed or until the 2-second flame proving
period begins. If the furnace control CPU selects high-heat
operation, the high-heat gas valve solenoid GV-HI is also
energized.
d. Flame-Proving - When the burner flame is proved at the
flame-proving sensor electrode FSE, the inducer motor IDM
switches to low-speed unless the furnace is operating in
high-heat, and the furnace control CPU begins the blower-ON
delay period and continues to hold the gas valve GV-M open. If
the burner flame is not proved within two seconds, the control
CPU will close the gas valve GV-M, and the control CPU will
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