Bryant Bruant 4 Way Gas 355AAV - Manual (Page 49)

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exchangers to heat more quickly, then restarts at the end of the
blower--ON delay period at low--heat or high--heat airflow
respectively.
The blower motor BLWM will revert to continuous--blower
airflow after the heating cycle is completed. In high--heat, the
furnace control CPU will drop the blower motor BLWM to
low--heat airflow during the selected blower--OFF delay period
before transitioning to continuous--blower airflow.
When the thermostat “calls for high--cooling”, the blower motor
BLWM will operate at high--cooling airflow. When the thermostat
is satisfied, the blower motor BLWM will operate an additional 90
seconds at high--cooling airflow before transitioning back to
continuous--blower airflow.
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 operation.
CONTINUOUS BLOWER SPEED SELECTION
FROM THERMOSTAT
To select different continuous--blower speeds from the room
thermostat, momentarily turn off the FAN switch or pushbutton on
the room thermostat for 1--3 seconds after the blower motor
BLWM is operating. The furnace control CPU will shift the
continuous--blower airflow from the factory setting to the next
highest CF selection airflow as shown in Fig. 47. Momentarily
turning off the FAN switch again at the thermostat will shift the
continuous--blower airflow up one more increment. If you repeat
this procedure enough, you will eventually shift the
continuous--blower airflow to the lowest CF selection as shown in
Fig. 47. The selection can be changed as many times as desired and
is stored in the memory to be automatically used following a power
interruption.
This feature is disabled when blower off delay is set for 180 sec.
HEAT PUMP
See Fig. 53--56 for thermostat connections.
When installed with a heat pump, the furnace control automatically
changes the timing sequence to avoid long blower off times during
demand defrost cycles. Whenever W/W1 is energized along with
Y1 or Y/Y2, the furnace control CPU will transition to or bring on
the blower motor BLWM at cooling airflow, low--heat airflow, or
the mid--range airflow, whichever is the lowest. The blower motor
BLWM will remain on until the main burners ignite, then shut OFF
and remain OFF for 25 seconds before coming back on at heating
airflow. When the W/W1 input signal disappears, the furnace
control begins a normal inducer post--purge period while changing
the blower airflow. If Y/Y2 input is still energized, the furnace
control CPU will transition the blower motor BLWM airflow to
cooling airflow. If Y/Y2 input signal disappears and the Y1 input is
still energized, the furnace control CPU will transition the blower
motor BLWM to low--cooling airflow. If both the Y1 and Y/Y2
signals disappear at the same time, the blower motor BLWM will
remain on at low--heat airflow for the selected blower--OFF delay
period. At the end of the blower--OFF delay, the blower motor
BLWM will shut OFF unless G is still energized, in which case the
blower motor BLWM will operate at continuous blower airflow.
COMPONENT TEST
The furnace features a component test system to help diagnose a
system problem in the case of a component failure. To initiate the
component test procedure, ensure that there are no thermostat
inputs to the control and all time delays have expired. Turn on
setup switch SW1--6 (See Fig. 37.)
NOTE: The component test feature will not operate if the control
is receiving any thermostat signals or until all time delays have
expired.
The component test sequence is as follows:
a. The furnace control CPU turns the inducer motor IDM
ON at medium speed and keeps it ON through step c.
b. After waiting 15 seconds, the furnace control CPU turns
the hot surface igniter ON for 15 seconds, then OFF.
c. The furnace control CPU then turns the blower motor
BLWM ON at mid--range airflow for 15 seconds, then
OFF.
d. After shutting the blower motor BLWM OFF, the
furnace control CPU shuts the inducer motor IDM OFF.
NOTE: The EAC terminals are energized when the blower is
operating.
After the component test is completed, 1 or more status codes (11,
25, 41, or 42) will flash. See Service Label on blower access panel
or Service/Status Code Instructions for explanation of status codes.
NOTE: To repeat component test, turn setup switch SW1--6 to
OFF and then back ON.
Step 6 — Adjustments
SET GAS INPUT RATE
Furnace gas input rate on rating plate is for installations at altitudes
up to 2000 ft. (610 M).
In the U.S.A., the input rating for altitudes above 2000 ft. (610 M)
must be reduced by 2 percent for each 1000 ft. (305 M) above sea
level.
In Canada, the input rating must be derated by 5 percent for
altitudes of 2000 ft. to 4500 ft. (610 to 1372 M) above sea level.
Adjust manifold pressure to obtain input rate.
Furnace input rate must be within +/--2 percent of input rate on
furnace rating plate.
1. Determine natural gas orifice size and manifold pressure for
correct input.
a. Obtain average heat value (at installed altitude) from
local gas supplier.
b. Obtain average specific gravity from local gas supplier.
c. Verify furnace model. Table 14 can only be used for
model 355AAV Furnaces.
d. Find installation altitude in Table 14.
NOTE: For Canadian altitudes of 2000 to 4500 ft. (610 to 1372
M), use U.S.A. altitudes of 2001 to 3000 ft. (610 to 914 M) in
Table 14.
e. Find closest natural gas heat value and specific gravity in
Table 14.
f. Follow heat value and specific gravity lines to point of
intersection to find orifice size and low-- and high--heat
manifold pressure settings for proper operation.
EXAMPLE: 0--2000 ft. altitude (0--610 M)
Heating value = 1050 Btu/cu ft.
Specific gravity = 0.62
Therefore: Orifice No. 45
Manifold pressure:
3.8--in. wc for high heat
1.6--in. wc for low heat
* Furnace is shipped with No. 45 orifices. In this example,
all main burner orifices are the correct size and do not need
to be changed to obtain proper input rate.
g. Check and verify burner orifice size in furnace. NEVER
ASSUME ORIFICE SIZE; ALWAYS CHECK AND
VERIFY.
355A