Carrier 17CB - Manual (Page 12)

MOTOR CURRENT CALIBRATION (Electronic
Capacity Control/Motor Drive)
1. Establish a steady motor current value for this
calibration. Open guide vanes manually
(capacity control to “Inc”) until full load
current is reached. Motor current calibration
(Fig. 8) may need to be turned counter­
clockwise to permit vanes to open further. Do
not exceed 105% of nameplate full load
amperes.
If system load is sufficient to maintain full
load current for a period of time, caUbrate at
this condition. With small loads, pull down to
and maintain design leaving chilled water
temperature (capacity control at “Hold”) and
calibrate at this condition.
Setting Operating Controls — Electronic
Fig. 8 — Capacity Control Module
(Electric Motor Drive)
2. Measure motor current at selected condition.
Determine its percentage of full load motor
current.
3. Use this percentage figure to set the electrical
demand adjustment (Fig. 8) per the following
table:
Percent of Full
Load Motor Current
105
85 or above
65 to 84
45 to 64
below 45
Electrical Demand
Adjustment Setting
100 percent
80 percent
60 percent
40 percent
Control cannot be
calibrated
4. Turn the motor current calibration adjustment
fully clockwise. The guide vanes will close part
way.
5. Turn the thermostat adjustment (Fig. 8) to
COOLER (fully counterclockwise).
6. Set capacity control at “Inc” position.
7. Slowly turn the motor current calibration
counterclockwise. Allow the guide vanes to
open until motor current reaches 5% above the
electrical demand setting.
NOTE; There is a time lag of several seconds
due to feedback capacitance in the motor
current circuit. When the motor current cali­
bration setting is adjusted, allow for this time
lag.
8. Check the foregoing motor current calibrations
with machine under “Auto” control as
follows:
a. Close vanes manually (capacity control to
DEC).
b. Turn capacity control to AUTO. Vanes
should stop opening at electrical demand
setting.
9. If control was calibrated at less than 100%
load, turn electrical demand adjustment setting
to 100%. Control is now automatically cali­
brated for 100% full load current.
10. If control cannot be calibrated with above
procedure, check voltage signal from signal
resistor in starter. At 100% full load current,
voltage between terminals 23 and 24 inside
control center must be 0.5 ± 0.1 volts. If not
in this range, check sizing of resistor in starter.
Both excess motor current and chilled
water temperatures below the thermostat set point
(Fig. 8) will override the capacity control setting.
If the capacity control knob is in the “Inc”
position, the guide vanes will stop opening. With
the knob in any of the other positions, the vanes
will close as needed.
The motor current limiting circuit operates in
two steps.
At 100% full load motor current, the vanes
will stop opening further. If the motor current
should increase to 105% due to some change in
load conditions, the vanes will close until the
motor current is reduced to about 102%.
If the motor current is reduced to 98% or
below, control again operates in response to chilled
water temperature.
The electrical demand adjustment permits the
operator to set the maximum current drawn by the
motor and thus minimize the electrical demand
rate during off-season operation.
CHILLED WATER CALIBRATION (Electronic
Controls)
1. Turn throttle range adjustment (Fig. 8 and 9)
fully clockwise.
A
i.
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