Units With Electro-Mechanical Controls; Low Speed Fan Adjustment; 2-Pin Dip Switch; Low Speed 2-Pin Dip Switch Settings - Carrier 50FC Series Service And Maintenance Instructions

Units with Electro-mechanical controls

The Fan Speed set up controls are located on the lower sec-
tion 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 Set
Up Label, add accessory Vdc to base unit Vdc in upper
portion of label. For electric heaters use only one adder.
(ex. 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 FC low fan
speed for 3 to 5 ton 50FC units set both dip switches to "OFF"
(0). For 6 ton 50FC 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
UNIT SIZE
(TONS)
DIP1
3, 4, 5 0
6 1
% OF USER SET
FAN SPEED
DIP2
0 100%
1 66%
Fig. 7 — UCB Fan Speed Controls
5
FAN SPEED SET UP CONTROLS