Carrier WeatherExpert 50LC14, Installation Instructions Manual, Page: 46 / 84

46
Low Ambient Cooling Operation Down to 40°F (4°C)
In Low Ambient RTU conditions when the temperature is be -
tween 55°F (13°C) and 40°F (4°C), the Low Ambient Switch
(LAS) will be active and the outdoor fans will run to the pre-set
factory outdoor-fan speed. When the temperature is greater than
65°F (18°C), the Low Ambient Switch will deactivate and the out -
door fans will run in the standard cooling mode. If the Outdoor
Fan Select Switch (see Fig. 66) is in the ON position, the outdoor
fans will run in the Fan Cycle Speed Mode (FCS) set to 250 rpm.
If the Outdoor Fan Select Switch is in the OFF position, the out -
door fans will run in the Minimum Fan Speed Mode (MIN) set to
160 rpm regardless of the cooling demand.
The 50LC 14-26 units have a SPST normally open Low Ambient
Switch wired across the TS and OF terminal and a jumper placed
across the PS terminal (see Fig. 67). When the LAS is active, the
switch will close making contact to the OF terminal. This is done
for units that require all outdoor fans to run at the same pre-set fac -
tory Low Ambient Speed.
Fig. 66 — Outdoor Fan Speed Select Switch
Fig. 67 — SPST Low Ambient Switch Schematic
Table 6 shows the low ambient temperature operation of the out -
door fan for each unit.
Table 6 — Low Ambient Temperature
Outdoor Fan Control
Heating
In the Heating Mode (W1 on the thermostat), power is applied to
the G and W1 terminal at the ISC board and energizes the first
state of electric heat. Upon more call for heat (W2 at the thermo -
stat), power is applied to the G and W2 terminal at the ISC board
and energizes the second state of electric heat. The VFD
controlled indoor fan will operate at high speed regardless of the
heating demand.
Economi$er
®
X (Factory-Installed Option)
EconoMi$er X is an economizer system available for 50LC 14-26
units. The factory-installed option consists of:
• Either a ultra low leak or a low leak economizer damper
assembly
• Direct-drive damper actuator with local equipment bus
communications
• W7220 economizer controller with keypad and display
• Supply air temperature sensor (20k ohm)
• Outdoor changeover condition sensor (either 20k ohm dry
bulb or enthalpy sensor)
UNIT INSTALLATION
All damper hardware and standard economizer control compo
-
nents except the enthalpy sensor are factory-mounted in their op -
erating location. Complete the unit installation by relocating the
enthalpy sensor (when provided; see below), then assembling and
mounting the unit’s outside air hood. Refer to the base unit’s in -
stallation instruction manual for directions on locating the hood
parts package and assembling the hood with filters.
ENTHALPY SENSOR RELOCATION
See the section Enthalpy Control Sensor Configuration on page 57
for a view of the enthalpy sensor and DIP switch settings. Locate
the enthalpy sensor on the side of the economizer housing; remove
mounting screws and save screws. Confirm the DIP switches are
set at OFF, OFF, OFF. Move the enthalpy sensor to the front face
of the economizer housing and mount per label.
W7220 ECONOMIZER CONTROLLER
The Honeywell W7220 economizer controller is used on electro-
mechanical units. The W7220 provides typical economizer func -
tions, including:
• Management of outside air damper for base unit Occupied
(damper open and modulating) and unit OFF or Unoccupied
status (damper closed)
• Free-cooling using all outside air when outdoor conditions
permit Integrated cooling operation using outside air and
mechanical cooling when required
• Demand Controlled Ventilation (DCV) for modulating ven -
tilation airflow according to space CO
2
level (requires fac -
tory-option or field-installed CO
2
sensor)
The W7220 control can also adjust the damper control points
during DCV or minimum ventilation operation as the indoor fan
speed is changed. This control function ensures that required
space ventilation airflow quantities are maintained during reduced
fan speed operation.
Additional control capabilities include automatic detection of new
sensors and detection of sensor failure or loss of communication.
The W7220 control module includes an integral user interface
with keypad and LCD display that permits direct input of setpoint
values and configurations, and displays status and alarms.
The W7220 controller is located in the RTU base unit’s Control
Box. See the Installation Instructions for this base unit for the loca -
tion of the Control Box access panel.
User Interface
The user interface consists of a 2-line LCD display and a 4-button
keypad on the front of the economizer controller.
Keypad
Use the four navigation buttons (see Fig. 68) to scroll through the
menus and menu items, select menu items, and to change parame -
ter and configuration settings.
50LC
SIZE
NO. OF
FANS
ON
NO. OF
FANS
OFF
SWITCH
OUTDOOR
FAN
SELECT
SWITCH
RPM
14 3 0 SPST Up 250
17 4 0 SPST Up 250
20 4 0 SPST Up 250
24 6 0 SPST Up 250
26 6 0 SPST Up 250
OF SPEED
SELECT
ON
FCS
MIN
OFF
JUMPER ON
LAS
SPST
PS PS
TS OF