Carrier 19CB - Manual (Page 10)

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a.
b.
9. If
Fig. 7 — Capacity Control Module
(Electronic Control)
Check the foregoing motor current calibrations
with machine under “Auto.” control as
follows'
Close vanes manually (capacity control to
“Dec”).
Turn capacity control to “Auto.” Vanes
should stop opening at electrical demand
setting.
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.
7) 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 hmiting circuit operates in
2 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. 7) fully
clockwise.
2. Turn chilled water thermostat until design
chilled water temperature is maintained. Mark
thermostat at this position. If capacity control
vanes hunt, turn throttle range adjustment
counterclockwise in small increments until
hunting ceases. Chilled water thermostat may
require resetting.
Setting Operating Controls — Pneumatic Capacity
Control
PILOT POSITIONER
ITEM DESCRIPTION
1 MAIN AIR CONNECTION (25 PSIG)
2 STARTING POINT ADJUSTMENT NUT
3 LEVER ARM
4 FOLLOWER SPRING
5 PILOT AIR CONNECTION
(FROM CONTROL CENTER)
Preparation:
a. Place jumper between field wiring terminal
and load limiting module terminal*^.
b. Open 25 lb air supply valve.
c. Remove cover from pilot positioner.
Calibration:
Rotate dial on chilled water thermostat to vary
pilot pressure. Observe pressure gage in pilot
supply line near pilot positioner and adjust starting
point nut (2) until piston operator begins to move
at 5 psi pilot pressure. Place follower spring (4) in
proper hole in level arm so that piston operator
opens 100% at 15 psi pilot pressure.
Completion:
Remove jumper from terminals and
Replace cover.
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