McQuay AGS 225D, Operating Manual

Page: 28 / 82

28 OM AGSD-1
Switches
All methods of disabling the chiller, except for the Override Stop switch, will cause a
normal pumpdown shutdown of any running circuits.
Rapid shutdown by the Override Stop switch without going through the pumpdown cycle is
undesirable and should only be used for an emergency shutdown or for manually and locally
disabling the unit after both circuits have gone through a normal shutdownand the
compressors have stopped.
The unit switch Q0, will perform a pumpdown and shutoff on all running compressors.
The system switches, Q1, Q2, (and Q3) will perform a pumpdown and shutoff on
compressors #1, #2, (or #3).
Unit Mode Selection
The overall operating mode of the chiller is set by the Unit Mode Setpoint with options of
COOL, COOL w/Glycol, ICE w/Glycol, HEAT, and TEST. This setpoint can be altered by
the keypad, BAS, and Mode input. Changes to the Unit Mode Setpoint are controlled by
two additional setpoints.
•
Available Modes Setpoint: Determines the operational modes available at any time
with options of COOL, COOL w/Glycol, COOL/ICE w/Glycol, and ICE w/Glycol.
•
Control Source Setpoint: Determines the source that can change the Unit Mode
Setpoint with options of KEYPAD, NETWORK, or SWITCHES.
When the Control Source is set to KEYPAD, the Unit Mode will stay at its previous setting
until changed by the operator. When the Control Source is set to BAS, the most recent BAS
mode request will go into effect even if it changed while the Control source was set to
KEYPAD or DIGITAL INPUTS.
Changing the Unit Mode Setpoint can be accomplished according to the following table.
NOTE: An “x” indicates that the value is ignored.
Control Source
Setpoint
Mode
Input
Keypad Entry
BAS
Request
Available Modes
Setpoint
Unit Mode
x x x x
COOL
COOL
x x x x COOL w/Glycol COOL w/Glycol
SWITCHES OFF x x COOL/ICE w/Glycol COOL w/Glycol
SWITCHES ON x x COOL/ICE w/Glycol ICE w/Glycol
KEYPAD x COOL w/Glycol x COOL/ICE w/Glycol COOL w/Glycol
KEYPAD x ICE w/Glycol x COOL/ICE w/Glycol ICE w/Glycol
NETWORK x x COOL COOL/ICE w/Glycol COOL w/Glycol
NETWORK x x ICE COOL/ICE w/Glycol ICE w/Glycol
x x x x ICE w/Glycol ICE w/Glycol
x x x x TEST TEST
Unit Test Mode
The unit test mode allows manual testing of controller outputs. Entering this mode requires
the following conditions.
•
Unit OFF input = OFF (i.e. entire chiller is shut down).
•
Manager password active.
•
Available Unit Mode setpoint = TEST
A test menu can then be selected to allow activation of the outputs. It will be possible to
switch each digital output ON or OFF and set the analog outputs to any value.