Cooling Mode; Continuous Blower Mode; Heat Pump Mode; Component Test - Bryant 345MAV Installation, Start-Up, And Operating Instructions Manual

a. Inducer Prepurge Period- As the inducer motor IDM
comes up to speed, the pressure switch contacts PRS
close, 24 vac power is supplied for a field installed
humidifier at the HUM terminal and the control begins a
15-second prepurge period.
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-
warm-up period is completed, the main gas valve relay
contacts GVR close to energize the gas valve GV, the
gas valve opens. The gas valve GV permits gas flow to
the burners where it is ignited by the Hot Surface Igniter
HSI. Five seconds after the GVR closes, a 2-second
flame period begins. The HSI igniter will remain ener-
gized until the flame is sensed or until the 2-second
flame proving period begins.
d. Flame-Proving- When the burner flame is proved at the
flame-proving sensor electrode FSE, the furnace control
CPU begins the blower-ON delay period and continues
to hold the gas valve GV open. If the burner flame is not
proved within two seconds, the control CPU will close
the gas valve GV, and the control CPU will repeat the
ignition sequence for up to three more Trials-For-
Ignition before going to Ignition-Lockout. Lockout will
be reset automatically after three hours, by momentarily
interrupting 115 vac power to the furnace, or by inter-
rupting 24 vac power at SEC1 or SEC2 to the furnace
control CPU (not at W, G, R, etc.)
If flame is proved when flame should not be present, the
furnace control CPU will lock out of Gas-Heating mode
and operate the inducer motor IDM until flame is no
longer proved.
e. Blower-On Delay- If the burner flame is proven, the
blower motor is energized on HEAT speed 66 seconds
after the gas valve GV is energized.
Simultaneously, the electronic air cleaner terminal
EAC-1 is energized and remains energized as long as the
blower motor BLWM is energized.
f. Blower-Off Delay- When the thermostat is satisfied, the
R-to-W circuit is opened, de-energizing the gas valve
GV, stopping gas flow to the burners, and de-energizing
the humidifier terminal HUM. The inducer motor IDM
will remain energized for a 15-second post-purge period.
The blower motor BLWM and air cleaner terminal
EAC-1 will remain energized for 90, 120, 150, or 180
seconds (depending on the blower-OFF delay selection).
The furnace control CPU is factory-set for a 120-second
blower-OFF delay.

2. Cooling Mode

(See Fig. 30 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
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 operating.
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. Cut jumper J2 to reduce
the cooling off-delay to 5 seconds. (See Fig. 33.)
When the igniter
—35—

3. Continuous Blower Mode

When the R-to-G circuit is closed by the thermostat, the
blower motor BLWM will operate on continuous-blower
speed (same as HEAT speed). Terminal EAC-1 is energized
as long as the blower motor BLWM is energized.
During a call for heat, the blower BLWM will stop during
igniter warm-up (17 seconds), ignition (7 seconds), and
blower-ON delay (66 seconds), allowing the furnace heat
exchangers to heat up more quickly, then restarts at the end
of the blower-ON delay period at HEAT speed.
In heating, the furnace control CPU will continue running
the blower motor BLWM at HEAT speed after the selected
blower-OFF delay period is completed.
When the thermostat calls for cooling , the blower motor
BLWM will operate at COOL speed. When the thermostat
is satisfied, the blower motor BLWM will operate an
additional 90 seconds on COOL speed before reverting
back HEAT speed. Jumper J2 can be cut to reduce the
cooling off-delay to 5 seconds. (See Fig. 31.)
When the R-to-G circuit is opened, the blower motor
BLWM will continue operating for an additional 5 seconds,
if no other function requires blower motor BLWM opera-
tion.
4. Heat Pump
When installed with a heat pump, the furnace control
automatically changes the timing sequence to avoid long
blower off times during demand defrost cycles. When the
R-to-W-and-Y or R-to-W-and-Y-and-G circuits are ener-
gized the furnace control CPU will continue to turn on the
blower motor BLWM at HEAT speed, and begin a heating
cycle. The blower motor BLWM will remain on until the
end of the prepurge period, then shut off for 24 seconds then
come back on at HEAT speed. When the W input signal
disappears, the furnace control begins a normal inducer
post-purge period and the blower switches to COOL speed
after a 3 second delay. If the R-to-W-and-Y-and-G signals
disappear at the same time, the blower motor BLWM will
remain on for the selected blower-OFF delay period. If the
R-to-W-and-Y signals disappear, leaving the G signal, the
blower motor BLWM will continue running the blower
motor BLWM at HEAT speed after the selected blower-
OFF delay period is completed.
A. Component Test
NOTE: The furnace control component test allows all compo-
nents to run for a short time; except the gas valve and humidifier
terminal HUM are not energized for safety reason. The EAC-1
terminal is energized when the blower is energized. This feature
helps diagnose a system problem in case of a component failure.
The component test feature will not operate if any thermostat
signal is present and the control and not until all time delays are
completed.
NOTE: Record the status code BEFORE opening the blower
access door and before shutting off power to the furnace. Opening
the blower access door will open the blower door switch and shut
off power within the furnace. When power to the furnace is shut
off by either method, the status code will be lost because the code
is not stored while power is removed for any reason.
To Begin Component Self-Test:
WARNING: Blower access panel door switch opens
115-v power to control center. No component operation
can occur. Caution must be taken when manually closing
this switch for service purposes. Failure to follow this
warning could result in electrical shock, personal injury,
or death.