Carrier 48TC series, Service And Maintenance Instructions

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*With 2SP FAN DELAY (Advanced Setup Menu) when in the economizing mode there is a delay for the high speed fan to try to satisfy the call for sec-
ond stage cooling by turning on the fan to high and opening the OA damper 100% before the first stage mechanical cooling is enabled.
†With stage 3 delay (STG3 DLY) in Advanced setup menu can turn on second stage of mechanical cooling Y2–O after the delay if the call for Y1–I and
Y2–I have not been satisfied.
ENTHALPY SETTINGS
When the OA temperature, enthalpy and dew point are below the
respective set points, the Outdoor Air can be used for economiz -
ing. Figure 80 shows the new single enthalpy boundaries in the
W7220. There are 5 boundaries (set points ES1 through ES5),
which are defined by dry bulb temperature, enthalpy and dew
point.
Refer to Table 37 for ENTH CURVE set point values.
The W7220 calculates the enthalpy and dew point using the OA
temperature and humidity input from the OA enthalpy sensor.
When the OA temperature, OA humidity and OA dew point are
all below the selected boundary, the economizer sets the econo -
mizing mode to YES, economizing is available.
When all of the OA conditions are above the selected boundary,
the conditions are not good to economize and the mode is set to
NO.
Figure 80 shows the 5 current boundaries. There is also a high lim -
it boundary for differential enthalpy. The high limit boundary is
ES1 when there are no stages of mechanical cooling energized and
HL (high limit) when a compressor stage is energized.
TWO-SPEED FAN OPERATION
The W7220 controller has the capability to work with a system us
-
ing a 2-speed supply fan. The W7220 does not control the supply
directly but uses the following input status to determine the speed
of the supply fan and controls the OA damper to the required posi -
tion, see Table 36.
The W (heating mode) is not controlled by the W7220 but it re -
quires the status to know where to position the OA damper for
minimum position for the fan speed.
The 2-speed fan delay is available when the system is pro -
grammed for 2-speed fan (in the System Setup menu item). The
2-speed fan delay is defaulted to 5 minutes and can be changed
in the Advanced Setup menu item. When the unit has a call for
Y1 In and in the free cooling mode and there is a call for Y2 In,
the 2-speed fan delay starts and the OA damper will modulate
100% open, the supply fan should be set to high speed by the
unit controller.
After the delay, one of two actions will happen:
• The Y2 In call will be satisfied with the damper 100%
open and fan on high speed and the call will turn off
OR
• If the call for additional cooling in the space has not been
satisfied, then the first stage of mechanical cooling will be
enabled through Y1 Out or Y2 Out.
Table 35 — Enthalpy Operation with DCV (CO
2
Sensor) — 2 Speed Fan
DEMAND
CONTROLLED
VENTILATION (DCV)
OUTSIDE AIR
GOOD TO
ECONOMIZE
Y1-I Y2-I
FAN
SPEED
Y1-O Y2-O OCCUPIED UNOCCUPIED
Below CO
2
Set
No
OFF OFF LOW 0v/Off 0v/Off VENTMIN Closed
ON OFF LOW 24v/On 0v/Off VENTMIN Closed
ON ON HIGH 24v/On 24v/On VENTMIN Closed
Yes
OFF OFF LOW 0v/Off 0v/Off VENTMIN Closed
ON OFF LOW 0v/Off 0v/Off
VENTMIN to
Full-Open
Closed to Full-Open
ON ON HIGH 24v/On 0v/Off
VENTMIN to
Full-Open
Closed to Full-Open
Above CO
2
Set
No
OFF OFF LOW 0v/Off 0v/Off
VENTMIN to
VENTMAX
Closed
ON OFF LOW 24v/On 0v/Off
VENTMIN to
VENTMAX
Closed
ON ON HIGH 24v/On 24v/On
VENTMIN to
VENTMAX
Closed
Yes
OFF OFF LOW 0v/Off 0v/Off
VENTMIN to
VENTMAX
Closed
ON OFF LOW 0v/Off 0v/Off
VENTMIN to
Full-Open
Closed to Full-Open
ON ON HIGH
DELAY*
24v/On
0v/Off*
VENTMIN to
Full-Open
Closed to Full-Open
Table 36 — Fan Speed
STATE FAN SPEED
OCC Low
Y1 Low
Y2 High
W High