Specifications
Space Temperature Reset Sensor (VAV Only)
—
An accessory space temperature sensor (T-55 or T-56 with-
out offset) is required. Space temperature reset is used to
reset the supply-air temperature set point of a VAV system
higher, as the space temperature falls below the Occupied
Cool set point. As the space temperature falls below the cool
set point, the supply-air temperature will be reset upward
as a function of the reset ratio. Reset ratio is expressed in
degrees change in supply-air temperature per degree of space
temperature change. A reset limit will exist which will limit
the maximum number of degrees the supply-air temperature
may be raised. Both the reset ratio and the reset limit are
user definable. The sequence of operation is as follows:
1. The on/off status of the unit supply fan is determined.
2. If the fan is on, the sequence will check if the system is
in Occupied mode.
3. If the system is in Occupied mode, the sequence will
determine if the reset option is enabled.
4. If the reset option is enabled, the sequence will read the
space temperature and compare it to the Occupied Cool
set point. If the temperature is below the Occupied Cool
set point, the algorithm will compute the reset value and
compare this value against the reset limit. If it is greater
than the reset limit, the sequence will use the reset limit
as the reset value.
NOTE: A computer equipped with Carrier network access
software (ComfortWorks™, Building Supervisor, or Service
Tool) or an accessory LID-2B is required to enable this
function.
Supply-Air Temperature Reset (VAV Only) — A
field-supplied 4 to 20 mA input signal enables the supply-air
temperature to be reset 0° to 20° F (0° or 11.2° C). The supply-
air temperature reset option does not need to be enabled.
VFD Control Via Field-Supplied 4 to 20 mA(Third
Party Transducer) —
To set the VFD for field-supplied
4 to 20 mA, the VFD must be powered up; however, since
it is located near the indoor air fan, operation of the fan is
not desirable. To disable the fan perform the following
procedure:
1. Open the indoor fan circuit breaker.
2. Remove the jumper between CC and ST on the terminal
strip of the VFD (see Fig. 50).
3. Move the jumper between CC and SS1 to CC and SS2
(JOG) on the terminal strip of the VFD.
4. Close the indoor fan circuit breaker. The VFD is pow-
ered, but the fan will not operate.
5. On the front of the VFD is a keypad and display which
will be used to turn off the PID. To access this field, press
the PRG key until the display reads J.PrG (Jump Fre-
quency Group Parameters). Press the ARROW key until
Fb.PI (Item 7, PID Set Point Control Select) is displayed.
Use the UP or DOWN arrow key to adjust the setting to
0. The default value is 0. See Table 2.
6. Open the indoor fan circuit breaker.
7. Replace the jumper between CC and ST on the terminal
strip of the VFD.
8. Close the indoor fan circuit breaker. The VFD is now pow-
ered and the fan will operate.
Table 2 — VFD Supply-Air Pressure Set Point
PRESSURE
CONTROL
(mA)
VFD
SET POINT
in. wg kPa
0.00 0.000 4.0 0
0.25 0.062 4.8 3
0.50 0.124 5.6 6
0.75 0.187 6.4 9
1.00 0.249 7.2 12
1.25 0.311 8.0 15
1.50 0.373 8.8 18
1.75 0.435 9.6 21
2.00 0.498 10.4 24
2.25 0.560 11.2 27
2.50 0.622 12.0 30
2.75 0.684 12.8 33
3.00 0.747 13.6 36
3.25 0.809 14.4 39
3.50 0.871 15.2 42
LEGEND
VFD — Variable Frequency Drive
50EJQ,EWQ UNITS
NOTE: Unit is shipped with default values that can be changed
through Service Tool or CCN software.
Cooling — On power up, the control module will acti-
vate the initialization software. The initialization software
reads DIP switch no. 1 position to determine CV operation.
Next, DIP switch no. 2 is read to determine if the control is
TSTAT or sensor type operation. The initialization
sequence: clears all alarms and alerts; re-maps the input/
output database for CV operation; sets maximum heat stages
to 2; and sets maximum cool stages to 3. The control module
reads DIP switch no. 3 and determines if the unit will use
expansion mode operation.
The TSTAT function performs a thermostat based control
by monitoring Y1, Y2, W1, W2 and G inputs. These func-
tions control stages: cool1, cool2, heat1, heat2, and the
indoor fan respectively. If the TSTAT function is not
selected, the control module determines the occupancy state
based on the system time schedules or with remote occupied/
unoccupied input. If Temperature Compensated Start is
active, the unit will be controlled as in the Occupied mode.
Occupied or unoccupied comfort set points must be
selected. Use of the space temperature offset input can also
be configured. The control module will set appropriate op-
erating mode and fan control. The control module will turn
on indoor fan if in Occupied mode or if the unit is in Un-
occupied mode and the space temperature is outside of the
unoccupied comfort set points (Unoccupied Heat or Unoc-
cupied Cool). The control module will then monitor space
temperature against comfort set points and control heating
or cooling stages as required. If the system is in the Occu-
pied mode, the economizer will operate as required. If the
system is in Unoccupied mode, the system will perform night-
time free cool and IAQ (indoor air quality) pre-occupancy
purge as required (when functions are enabled via software).
Whenever the DX (direct expansion) cooling is requested,
the outdoor fan will operate.
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