McQuay WGS130AA: WGS140AW, Operating Manual

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OM WGS-5 WGS 130A to 190A 41
Unit Enable
Enabling and disabling the chiller is controlled by the Unit Enable Setpoint with options of
OFF and ON. Enabling allows the unit to start if there is a call for cooling and also starts
the evaporator pump.
This setpoint (in other words, enabling the unit to run) can be altered by the:

Unit OFF input (unit On/Off switch)

a field installed remote stop switch

a keypad entry

a BAS request
The Control Source Setpoint determines which sources can change the Unit Enable Setpoint
with options of SWITCHES, KEYPAD or NETWORK.
Changing the Unit Enable Setpoint can be accomplished according to the following table.
NOTE : An “x” indicates that the entry is ignored.
Table 16, Unit Enable Combinations
Unit On/Off
Switch
Control Source
Setpoint
Remote
Stop Switch
Key-pad
Entry
BAS
Request
Resultant
Unit Enable
Status
OFF x x x x OFF
ON/OFF SWITCHES OFF x x OFF
ON SWITCHES ON x x ON
ON KEYPAD x OFF
x OFF
ON KEYPAD x ON x ON
ON NETWORK x x OFF OFF
ON NETWORK OFF x x OFF
ON NETWORK ON x ON ON
Example:
1.
If the Control Source is set to “Switches”, enabling is controlled by the field-installed
remote stop switch. If the unit-mounted On/Off switch is either On or Off, the unit will
be disabled if the remote switch is Off. If the unit-mounted On/Off switch is On, the
unit will be enabled if the remote switch is On.
Chiller Control Source Options:
Set Unit Setpoints Screen #1 (shown below) has three fields: “Enable”, “Mode” and
“Source.”
Unit Setpoints
SET UNIT SPs (1)
Enable=On
Mode= COOL
Source = KEYPAD
The Enable field can only be used with Source = Keypad, to enable and disable the chiller
through the key pad, any other control inputs including unit and pumpdown switches and
BAS controls are ignored. The Enable field toggles between On and Off using the Up or
Down key on the controller.
1. The Mode field is an informational display, showing the active control mode of the
chiller. It is used as an input only when the source is set to keypad, only then can this
field be changed manually.
2. The Source field has three options, “SWITCHES”(default), “KEYPAD”, and “BAS
NETWORK”.