CONTROL
The control panel and compressor lube box contain most of
the operating and protective controls. The control center is
completely prewired and most adjustable controls have been
set during the factory test procedure.
Inspection of the control panel will reveal that it is divided
into three functional sections as shown in Figure 4.
TEMPERATURE SECTION
The temperature section contains the control module and
several thermostats with adjustments accessible with the
panel door open.
RELAY SECTION
The relay section is located behind the large left front door
with the McQuay logo. This section contains the opsrating
and safety relays and wiring terminal strip. Most relays are
plug-in type and can easily be removed for servicing.
SWITCH SECTION
Mounted in the lower section front panel are pressure gauges,
indicator lights, RESET button and the unit ON/OFF switch.
Behind this front panel is the switch section containing several
safety/operating switches and the reset pushbutton switches,
CONTROL MODULE
The McQuay solid-state capacity control module provides
temperature control and current limit control and is
equipped with several auxiliary features which provide the
operator with considerable flexibility in system control.
Two switches provide the operator with the options of
automatic or manual load/unload control. The switch posi-
tions are:
AUTO This position provides for automatic operation
of the control module to load or unload the
compressor to control water temperature leav-
ing the chiller.
M A N . Disconnects the automatic temperature con-
trol functions to permit manual control.
LOAD With switch in MAN, the SB loading solenoid
can be manually energized.
U N L O A D . With switch in MAN, the SA unloading
solenoid can be manually energized.
Indicator lights on the module will function as follows:
Red will light during unloading control action, green will light
during loading and amber will light when the load action is
overridden by the current limit control. Red and green can-
not light simultaneously nor can amber and green. Red and
amber indicate current limit has been exceeded by 5% of full
load and will signal “unload” until current is reduced to the
setpoint. Current limit will override manual load control.
A pulse rate adjustment is provided on the control module
to provide a means of matching load or unload speed to suit
the system size. Pulse rate can be set over the range of 2
to 25 pulses per minute and is effective only when the
chilled water temperature is within
F of setpoint. In a large
volume chilled water system a lower pulse rate (i.e., 8
pulses/minute) will provide adequate control response. Con-
versely a higher pulse rate in a small volume system will allow
CENTER
FIGURE 5. CONTROL MODULE
Load Light
Unload Light (Red)
Manual/Auto
Switch
Load/Unload
Water
Setting
Pulse
Rate
Adjustment
Current
Limit
C a l i b r a t i o n - .
Ramp
Start
Point
Ramp Time
Setting
the control to react quickly to temperature changes.
The controller is also equipped with a Ramp-up function
which can be adjusted to control the loading of a compressor
at start-up. The Start Point setting determines the point at
which controlled loading begins; the Ramp Time setting
establishes the time of controlled loading.
The adjustment knob marked “ % Current” would normal-
ly be positioned at 100% to permit the compressor to fully
load. If the operator desires to limit the motor amperes or com-
pressor capacity for any reason, this control can be set to
limit the motor current to any point between 30% and 100%.
The “Temperature” knob permits setting the chilled water
control point to the desired temperature.
Setting and calibration procedures for all functions of the
control module are detailed in the adjustments section of this
manual.
IM 307 / Page 9
