Capacity Control; Controller - Carrier 16JT Series Start Up & Operation Manual

Normally closed 4X contacts energize the Cycle- Guard™
valve to transfer refrigerant into the solution for dilu-
tion. The refrigerant pump and Cycle-Guard valve will
continue to be energized until the evaporator refrigerant
drops to the dilution level switch, which opens to de-
energize the refrigerant pump delay start timer (62T2).The
normally open timer contacts then stop the Cycle-Guard
valve and refrigerant pump. (Normally open 1X1 con-
tacts transferred control of the 62T2 timer from the evapo-
rator low-level switch to the dilution level switch when
1X1 was deenergized.)
When shutdown timer (62T1) times out after about
15 minutes, its contact opens to deenergize interlock re-
lays (1Y1 and 1Y2). Normally open 1Y2 contacts stop
the solution pump(s), as well as refrigerant pump and
Cycle-Guard valve if they have not already stopped. The
chilled water pump, cooling water pump, and cooling
tower fan also stop if they are tied into the chiller con-
trol circuit for auto. start/stop. When 62T1 times out, it
also shuts off the Dilution light.
8. The Stop button may be depressed to silence the buzzer,
turn off the fault indicator light, and reset the control cir-
cuit for restart; or, the Alarm Buzzer stop button
(3-BZ) may be depressed to silence the buzzer while the
control circuit remains in the shutdown alarm mode for
troubleshooting.
Capacity Control —
This is the controller that governs
the positioning of a capacity control valve and senses the
leaving chilled water temperature to determine the required
valve positioning. This valve regulates the flow of steam or
hot water to the generator, matching machine capacity to the
load, and maintains the selected chilled water temperature.
At full-load conditions, the capacity control valve is wide
open. As the load is reduced and the chilled water tempera-
ture starts to fall below design temperature, the valve throttles
the steam or hot water flow until, at no-load condition, the
valve is fully closed.
During start-up and shutdown periods, and with pro-
longed Cycle-Guard operation, the chiller control circuit over-
rides the signal to the steam valve to limit the valve opening.
The 16JT is available with either electronic or pneumatic
capacity control valve actuators, but both are positioned by
a microprocessor-based controller.
A temperature sensor inserted in the chilled water outlet
pipe continuously measures chilled water temperature and
provides a proportional signal to the controller in the ma-
chine control panel. The signal is electronically converted
by the controller which provides a variable signal for the
valve actuator.
CONTROLLER — The microprocessor-based controller can
be field programmed by using its own interface keys, dis-
play, and alternate inputs and outputs for many control varia-
tions, but is normally set up for proportional valve position-
ing in direct relationship to changes in the leaving chilled
water temperature.
When the AUTO. mode has been selected on the control-
ler AUTO.-MAN. button for normal automatic operation, both
the temperature control set point and the actual chilled water
temperature are shown on the controller display. The control
temperature set point can be raised or lowered in that mode
by pressing the up or down arrows on the controller.
When the MAN. mode has been selected on the controller
AUTO.-MAN. button, the control signal to the capacity con-
trol valve is displayed as 0 to 100% open, and the valve can
be manually opened or closed in that mode by pressing the
up ( ) or down ( ) arrows on the controller.
Electronic Valve Actuator (Fig. 17) — The proportional mil-
liamp output signal from the controller is supplied directly
to the electronic valve actuator for positioning control. When
safety device relay (4X) is deenergized in a chiller shutdown
condition, its contacts remain open so that the actuator sees
a ''0'' amp signal and remains closed. When the load limiter
relay (LIX) is deenergized during chiller start-up or Cycle-
Guard operation, the current limiter is in control and pro-
vides a preset control signal to hold the actuator at a mid-
open position for a preset time delay period.
LEGEND
Wiring Terminals
NOTE: See Fig. 10 for Control Circuit Connections.
Fig. 17 — Electronic Valve Actuator
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