Dunham-Bush ACDX, Installation, Operation And Maintenance Instructions

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ELECTRICAL CONTROLS (Cont'd)
Load/Unload/Fast Unload Solenoid
Valves
16TAS - Load Limit Thermostat (Optional)
The load/unload solenoid valves (A Gen) This thermostat prevents loading of the
modulate to the compressor slide valve compressor(s) when return water
during normal operation in response to temperature is above the dial setting. The
commands from 4TAS or microcomputer factory setpoint is 65
E
F.
controller.
The fast unload solenoid is activated (A Gen) The lead/lag control helps equalize run
during the first 30 seconds of compressor time on the two compressors by alternating
operation to insure that the compressor is the compressor that starts first (lead
fully unloaded. compressor). When the unit is shut down
Door Latch Solenoid (Optional) customer control contacts are opened, the
The door latch solenoids are used to hold lead/lag control will alternate the lead
the control and power panel doors closed compressor. Thus the lag compressor will
when power is applied to the unit. The be come lead and start first at the next call
control panel door solenoid can be for cooling.
temporarily de-energized with a key to
allow opening of the door. This allows
VM - Voltmeter (Optional)
access to the microcomputer keyboard/ The voltmeter along with the voltmeter
display or 4TAS temperature controller. transfer switch allows monitoring of the 3
Hot Gas Bypass Solenoid (Optional) phase voltage is shown on the meter.
This solenoid is energized under light NOTE: Refer to the unit wiring diagram for operation
load conditions. The hot gas reduces and safety control settings.
machine capacity to help prevent short
cycling of the compressor.
FIELD CONTROL WIRING
CO - Convenience Outlet (Optional) In addition to 3 phase power and 115 volt control
The convenience outlet is a 15 amp, 115 power supplies, the following control interlock wiring
volt duplex outlet. This allows easy is recommended. The "as built" control schematic,
access to 115 VAC power by service provided with the unit, provides detailed information.
personnel for small electrical tools. Typical control schematics are as shown on pages 27
1TAS - Motor Overload Protection
Compressor overload protection is 1) Unit Control Contact - Unit on-off control should be
provided by a solid state device (1TAS) done through the terminals shown on the wiring
that monitors internal motor temperature. diagram. An open contact shuts down the unit.
If the maximum motor temperature is Time clock, night shut down, and energy
exceeded, the compressor will shutdown. management shut down should all be done from
To reset 1TAS, open the control switch these terminals and contacts should be applied in
for 5 seconds. series. Shielded wire should be used. Ground the
UVR - Undervoltage Relay 2) Flow Switch - The flow switch contacts should be
Protects the unit from the following installed between the terminals shown on the
electric supply malfunctions: under- wiring diagram for the flow switch.
voltage, phase reversal and single 3) Chilled Water Pump Interlock (CWP) - An auxiliary
phasing. If the UVR trips, a control relay switch from the chilled water pump contactor
will de-energize and open the control should be installed between the terminals shown
circuit. A LED light, located on the UVR, on the wiring diagram. This helps ensure chilled
will indicate a normal power supply. water pump operation before the unit is started.
SCR - Fan Speed Control (Optional) water pump must be worked out by the system
The fan speed control varies the speed of designer. It is necessary for the pump to be on
the fan, depending on head pressure. during any compressor operation. However, it is
With a discharge pressure of 140 psig or likely that the pump should remain on throughout
below, the fan is at minimum speed. As all occupied operation or even at night for freeze
discharge pressure rises, the fan speed is protection.
increased proportionally until it reaches
full speed at 200 psig. See fan cycling
For microcomputer controlled units, the chilled
control section. water pump contacts shown on the wiring diagram
15
LLC - Lead/Lag Control (Optional)
because the load is satisfied or the
phase voltages. The switch selects which
thru 31.
shield at the control panel only.
4) Chilled Water Pump - The control of the chilled
should be used in the pump control circuit. These
contacts stay closed whenever the unit is enabled
(see item 1) and the internal schedule of operation