28
above the CO
2
set--poin t, the minimum pos ition of the
damper will be increased proportionally. As the CO
2
level
decreas es b ecause of the in creas e of fresh air, the
outdoor--air damper will be proportionally closed. For
economizer operatio n, there must be a thermostat call for the
fan (G). If the unit is occupied and the fan is on, the damper
will operate at minimum positio n. Other w is e, the damper
will be closed.
Low Ambient Cooling Operation down to 40_F(4_C) —
In Low Ambient RTU conditions when the temperature is
betwee n 55_F(13_C) and 40_F(4_C), the Low Ambient
Switch (LAS) will be active and the outdoor fans wil l 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 outdoor fans will
run in the standard cooling mode. If the Outdoor Fan
Select Switch (see Fig. 42) 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 Sel ect Switch is in the
OFF position, the outdoor fans will run i n the Minimum
Fan Speed Mode (MIN) set to 160 rpm regardless of the
cooling dem and.
LC Size 07 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. 43).
When the LAS is active, the switch will close making
conta ct to the OF terminal. This is done for units that
require all outdoor fans to run at the same pre--set factory
Low Ambient Speed.
OF SPEED
SELECT
ON
FCS
MIN
OFF
a48--- 9341
Fig. 42 -- Outdoor Fan Speed Select Switch
JUMPER ON
LAS
SPST
PS PS
TS OF
C13328
Fig. 43 -- Schematic of SPST Low Ambient Switch
The Low Ambient Temperature Outdoor Fan Control
Table (below) shows the operation of the outdoor fan for
size 07 units.
Table 4 – Low Ambient T em peratur e Outdoor Fan Control
LC Size
No. of
Fans On
No. of
Fans Off
Switch
Outdoor Fan
Sele ct Switch
RPM
07 2 0 SPST Up 250
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 thermostat), 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
dema nd.
EconoMi$er
R
X (Factory--Installed Option)
EconoMi$e r X i s an economizer system which is available
for 50LC 07 units.
The factory--installed option consists of:
S Either a Low leak or a Standard leak economizer
damper assembly
S Direct--drive damper actuator with local equipment bus
communications
S W7220 economizer controll er wit h keypad and display
S Supply Air Te mperature sensor (20K ohm)
S Outdoor changeover condition sensor (either 20K ohm
dry--bulb or ent halpy sensor)
Unit Installation —
All damper hardware and standard economizer control
components except the enthalpy sensor are factory--mounted
in their operatin g 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 installation instruction manual for
directions on locating the hood parts package and
assembling the hood with filters.
Enthalpy Sensor Relocation —
See Fig. 52 for view of the enthalpy sensor . 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 (see Table 12). Move the
enthalpy sensor to the front face of the economizer housing
and mount per label.
W7220 Economizer Controller
The economizer controller used on electro--mechanical units
is the Honeywell W7220.
The W7220 provides typical economizer functions,
including:
S Management of outside ai r damper for base unit
Occupie d (damper open and modulating) and unit OFF
or Unoccupied status (damper closed)
S Free--cooling using all outside air when outdoor
conditions permit Integrated cooling operation using
outside air and mechanical cooling when re quired
S Demand Controlled Ventilation (DCV) for modulating
ventilation airflow according to space CO
2
leve l
(requires factory--option or field--installed CO
2
sensor)
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