Bryant 395CAV - Manual (Page 11)

CAUTION: This furnace is equipped with a manual
reset limit switch or fuse link in the gas control area. The
switch or fuse link opens and shuts 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 problem and reset the
switch or replace the fuse link.
Before operating the furnace, check each manual reset switch for
continuity. If necessary, press the button to reset the switch.
The blower compartment door must be in place to complete the
115-v circuit to the furnace.
II. SEQUENCE OF OPERATION
CAUTION: Furnace control must be grounded for
proper operation, or control will lockout. Control is
grounded through green wire routed to gas valve and
burner bracket screw.
Using the schematic diagram shown in Fig. 11, follow the
sequence of operation through the different modes. Read and
follow the wiring diagram very carefully.
NOTE: If there is a power interruption and any thermostat call,
the control initiates a 90-sec blower only on period before starting
another cycle.
1. Heating mode
When the wall thermostat “calls for heat,” the R-W circuit
closes. The furnace control performs a self-check, verifies
the pressure switch contacts are open, and starts inducer
motor.
a. Prepurge period—As the inducer motor comes up to
speed, the pressure switch contacts close to begin a
15-sec prepurge period.
b. Igniter warm-up—At the end of the prepurge period, the
igniter is energized for a 17-sec igniter warm-up period.
c. Ignition sequence—When the igniter warm-up period is
completed, the gas valve opens, permitting gas flow to
the burners where it is ignited. After 5 sec, the igniter is
de-energized and a 2-sec flame-sensing period begins.
d. HUM terminal is energized with the gas valve. See
Accessories in the Electrical Connections section.
e. Flame-sensing—When burner flame is sensed, the con-
trol begins the blower on delay period and continues
holding the gas valve open. If burner flame is not sensed,
the control closes the gas valve and repeats ignition
cycle.
NOTE: Ignition sequence will repeat 3 additional time before a
lockout occurs. Lockout automatically resets after 3 hrs, or can be
manually reset by turning 115–v off (not at thermostat) for 3 sec
minimum, then on again.
f. Blower on delay—Forty-five sec after burner flame is
proven, the blower motor is energized on heating speed.
Simultaneously, the humidifier and electronic air cleaner
terminals (HUM and C
OM -24V for humidifier, EAC-1
and EAC-2 for electronic air cleaner) are energized. If
jumper is on pin 6 and pin 9, blower on delay is 66 sec.
g. Blower off delay—When the thermostat is satisfied, the
circuit between R-W is broken, de-energizing the gas
valve stopping gas flow to the burners. The blower
motor and EAC remain energized 90, 135, 180, or 225
sec (depending on the blower off-time selection). The
furnace is factory set for a 135-sec blower off delay.
h. Post-purge—The inducer motor remains energized 5 sec
after the burners are extinguished. If jumper is on pin 6
and pin 9, the post-purge period is 15 sec.
2. Cooling mode
When the thermostat “calls for cooling,” R-G and R-Y
circuits close. The R-Y circuit starts the outdoor condensing
unit and the combined R-Y and R-G circuits start the
furnace blower motor on cooling speed. The EAC-1 termi-
nal is energized with 115–v when the blower is operating on
cooling speed.
When the thermostat is satisfied, R-G and R-Y circuits are
broken. The furnace blower and EAC continue operating on
cooling speed for an additional 90 sec.
NOTE: EAC-1 terminal is energized with 115v whenever blower
operates.
3. Continuous blower mode
When the R-G circuit is made, the blower motor operates on
heating speed. During a call for heat, the blower stops,
allowing the furnace heat exchangers to heat up more
quickly, then restarts at the end of the 45-sec blower on
delay period. If jumper is on pin 6 and pin 9, the blower on
delay is 66 sec.
The blower reverts to continuous operation after the heating
cycle is completed.
When the thermostat “calls for cooling,” the blower oper-
ates on cooling speed. When the thermostat is satisfied, the
blower operates an additional 90 sec before reverting back
to continuous operation on heating speed.
4. Heat pump mode
When installed with a heat pump, the furnace control
automatically changes the timing sequence to avoid long
blower off time during demand defrost cycles. When the
W-Y or W-Y-G thermostat inputs are received at the same
time, the control changes the blower to heating speed or
starts the blower if it was off, and begins a heating cycle.
The blower remains on until the end of the prepurge period,
then shuts off until the end of the ignition warm-up and trial
for ignition periods (a total of 24 sec). The blower then
comes back on at heating speed.
When the W input signal disappears, the control begins the
normal inducer post-purge period and the blower changes to
cooling speed after a 1-sec delay. If the W-Y-G signals
disappear at the same time, the blower remains on for the
selected heating blower off delay period and the inducer
goes through its normal post-purge period. If the W-Y
inputs should disappear, leaving the G signal input, the
control goes into continuous blower and the inducer re-
mains on for the normal post-purge period.
Anytime the control senses false flame, the control locks
out of the heating mode. This occurs because the control
cannot sense the W input due to the false flame signal, and
as a result, sees only the Y input and goes into cooling
mode, blower off delay. All other control functions remain
in standard format.
NOTE: EAC-1 terminal is energized whenever blower operates.
HUM terminal is only energized when gas valve is energized.
III. START-UP PROCEDURES
1. Purge gas lines—After all connections have been made,
purge the lines and check for leaks.
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