Carrier 50LC 07, Service And Maintenance Instructions, Page: 52 / 100

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W7220 input OCC remains energized; the outside air
damper remains in MIN POS L. If ISC terminal G is also
de--energized with Y1, indicating AUTO Fan operation,
then the supply fan motor will stop. The W7220 input at
OCC is removed; the outside air damper closes.
If the space temperature continues to rise, the thermostat will
call for second stage cooling; ISC terminal Y2 is also
energized. The supply fan motor shifts to MED Speed.
Outside air damper position will remain in MIN POS L,
second stage cooling starts.
As space temperature falls, the thermostat will remove its
call for second stage cooling; ISC terminal Y2 call is
removed. The supply fan motor shifts back to Low Speed.
The outside air damper remains at MIN POS L and the
ISC board will stop second stage mechanical cooling.
If the space temperature continues to rise, the thermostat will
call for third stage cooling; ISC terminal Y--3 is also
energized. The supply fan motor shifts to High Speed. The
outside air damper position will shift to MIN POS H, third
stage cooling starts.
As space temperature falls, the thermostat will remove its
call for third stage cooling; ISC terminal Y3 call is
removed. The supply fan will shift to Medium Speed.
The outside air damper position is repositioned to MIN
POS L and stop third stage mechanical cooling.
When free cooling is available as determined by the
appropriate changeover command (outdoor dry bulb,
outdoor enthalpy, differential dry bulb or differential
enthalpy), a space thermostat call for Stage 1 Cooling
energizes ISC terminals G and Y1; supply fan motor starts
and runs in High Speed. The G demand is received at
W7220 input OCC; outside air damper moves to MIN
POS L. The Y1 demand is received at W7220 terminal
Y1--I. The W7220 economizer control will modulate the
outside air damper open and closed to maintain the unit
cooling supply air temperature at setpoint MAT SET
(default 53
_
F (12
_
C)). Compressor will not run.
During free cooling operation, a supply air temperature
(SAT) above MAT SET will cause the outside air damper
to modulate between MIN POS L setpoint and 100%
open. As SAT decreases and approaches setpoint MA LO
SET (default 45
_
F (7
_
C)), the outside air damper will
maintain at the MIN POS L setting. With SAT below MA
LO SET, the outside air damper will be closed or at
minimum (see FREEZE POS) When SAT rises to MA LO
SET plus 3
_
F, the outside air damper will re--open to MIN
POS L setting.
Should 100% outside air not be capable of satisfying the
space cooling load, space temperature will rise and the
thermostat will call for second stage cooling; ISC terminal
Y2 is also energized. The supply fan motor remains at
High Speed. Outside air damper position will remain at
MIN POS L, starting second stage cooling (Compressor 1
operation). Damper will modulate to maintain SAT at
MAT SET concurrent with Compressor 1 operation.
Table 18 – W7220 Input/Output without CO
2
Sensor
INPUTS
Ref:
FAN
SPD
(a)
OUTPUTS
DEMAND
CONTROL
VENTILATION
OUTSIDE AIR
Good to
economize?
Y1---I Y2---I
Mechanical Cooling Stage
Occupancy
OCC Yes OCC No
Y1---O/1ST Y2---O/2ND Outside Air Damper Position
NO CO
2
SENSOR
No
Off Off Low 0---v/Off 0---v/Off MIN POS L Closed
On Off Low 24---v/On 0---v/Off MIN POS L Closed
On On High 24---v/On 24---v/On MIN POS H Closed
Yes
Off Off Low 0---v/Off 0---v/Off MIN POS L Closed
On Off Low 0---v/Off 0---v/Off
Modulating:
MIN POS L to
Full---Open
Modulating:
Closed to
Full---Open
On On High
2SP DELAY (b);
24v/On
0---v/Off (c)
Modulating:
MIN POS H to
Full---Open
Modulating:
Closed to
Full---Open
(a)
Fan Speed for reference only; tins is not an input or output function of the W7220
(b)
See Menu ADV SETUP ---> 2SP FAN DELAY for details
(c)
See Menu ADV SETUP ---> STG# DLY. With Stage 3 delay enabled, control can turn on 2
nd
stage of cooling Y2---O after delay if the call for Y2---I has not
been satisfied.