Bryant 547K 04-07 Series Service And Maintenance Instructions page 5

EVALUATING MOTOR SPEED
The direct drive ECM blower motor uses a constant speed de-
sign. Motor speed is controlled by a 0-10 vdc signal, where
10 vdc is equal to the motor's maximum rpm.
SELECTING FAN SPEED
All units come factory set for 9.0 vdc or approximately 90% of
the motor's maximum speed. Fan speed should be set per job
specification cfm (cubic feet per minute) and ESP (external
static pressure) required and per Fan Speed Set Up label in-
cluded on the unit's high voltage cover. In some cases, the Fan
Speed Set Up label may already include the field setting if unit
was previously installed. Check the box on the lower half of
the label to see if the field voltage setting was filled in and if
so, set fan speed to that voltage. Otherwise see detailed instruc-
tions below.
NOTE: Fan Speed Set Up is for full load airflow. If the unit has
multiple stages of cooling, low cool and ventilation may operate at
lower fan rpms. This offset is factory set and controlled by the
UCB. If fan speed verification is being done with a strobe, fan
speed should be verified in all unit operation modes.
Units with Electro-mechanical controls
The Fan Speed Set Up controls are located on the lower section
of the Unit Control Board (UCB). See Fig. 7 for location.
1. Check the job specifications for the cfm (cubic feet per
minute) and ESP (external static pressure) required.
2. Using the chart on the Fan Speed Set Up labels (see
Fig. 8), calculate the vdc from the cfm and ESP for the
base unit.
3. If installing any accessories listed at the bottom of the Fan
Speed Set Up label, add accessory vdc to base unit vdc in
upper portion of label. For electric heaters use only
1 adder (e.g., 2 stage heater uses only 2 stage adder, not
1 stage plus 2 stage).
NOTE: The Fan Speed Set Up labels are located on the High Volt-
age cover in the Control Box.
4. Connect a multimeter to the vdc terminals on the UCB.
5. Set the Range Switch to either A, B, or C per the Switch
Range table.
6. Using a straight blade screwdriver turn the vdc control dial
to fine tune the vdc reading.
7. Record the reading in the Field Setting field.
Low Speed Fan Adjustment
2-Pin DIP Switch
The Low Speed 2-Pin DIP switch is located near the center of
the UCB. See Fig. 7.
When replacing UCB, the board will be shipped as default
without a low speed selected. To select correct 547K low fan
speed for 3 to 5 ton 547K units, set both DIP switches to
"OFF" (0). For 6 ton 547K units set both DIP switches
"ON" (1). See Table 1. The DIP switch positions can also be
found on the unit's control label diagram.
Table 1 — Low Speed 2-Pin DIP Switch Settings
LOW SPEED
DIP1 DIP2
0 0
0 1
1 0
1 1
Fig. 7 — UCB Fan Speed Controls
5
PERCENTAGE OF USER SET
FAN SPEED
100%
88%
75%
66%
Fan Speed Set Up Controls