Carrier 50FCQ 04-07 Series Service And Maintenance Instructions page 5

EVALUATING MOTOR SPEED
The direct drive ECM blower motor uses a constant speed design.
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 specifi-
cation cfm (cubic feet per minute) and ESP (external static pres-
sure) required and per Fan Speed Set Up label included on the
unit's high voltage cover. In some cases, the Fan Speed Set Up la-
bel may already include the field setting if unit was previously in-
stalled. 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 instructions 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 50FCQ low fan speed for
3 to 5 ton 50FCQ units, set both DIP switches to "OFF" (0). For
6 ton 50FCQ 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