Dunham-Bush ACDX, Installation, Operation And Maintenance Instructions

Page: 14 / 44

Stage 2 Starting low, pressure switch (9PS-2) begins timing. If suction
Subsequent to the start of Compressor No. 1 an pressure does not rise above setpoint within 120
approximate five minute time delay is incorporated seconds, the compressor will be shut down.
into the microprocessor. After this time delay, and a
further call for cooling, the second step of the staging
Timer (7TR-2) will energize the fast unload solenoid
thermostat (4TAS) will close. This will energize relay (6SOL) for 30 seconds then energize relay (3CR).
(9CR). If all the safety controls and switches are
closed, (see "Safety Control" section for more details)
Upon energizing relay (3CR), the NO contacts are
the control circuit for Compressor No. 2 will energize, closed, allowing the thermostat (4TAS) to energize the
allowing the compressor start and energizing switches load solenoid (4SOL) and the unload solenoid (8SOL)
(1M1-1 and 2M1-2) open the oil heater and activate upon demand.
the fan control circuit. If suction pressure is
SHUTDOWN SEQUENCE
Stage 2 Shutdown Stage 1 Shutdown
After both compressors have unloaded fully and the If the leaving water temperature is still lower than the
leaving water temperature is still lower than the setpoint, the first step of the thermostat (4TAS) will
setpoint, the second step of the thermostat (4TAS) will open and de-energize relay (8CR). This will close the
open and de-energize relay (9CR) providing an liquid line solenoid (1SOL) and turn off Compressor
approximate three minute time delay integral with the No. 1 as long as it has run for approximately three
microprocessor, has expired subsequent to the start minutes. Compressor No. 1 will not be able to restart
of Compressor No. 2. This will close the liquid line for five minutes.
solenoid (5SOL) and turn off Compressor No. 2.
Compressor No. 1 will load and unload as required.
Compressor No. 2 will not be able to restart for five
minutes due to integral time delays.
SAFETY CONTROLS
The unit is protected by the following safety controls: 8. Water Flow Switch (FLS)
1. High Pressure (1PS) 9. Fan Circuit Breakers (CB)
2. Low Pressure (9PS) 10. Compressor Circuit Breakers (CB) (200/230V
3. High Discharge/Oil Temperature (12TAS) only)
4. Compressor Solid State Module (1TAS)
5. Low Water Temperature/Freeze (2TAS) If any of these devices should open due to abnormal
6. Compressor Starter Overloads (MOL) (200/230V conditions, the compressor(s) will automatically stop.
only) All controls must be manually reset, except the Under
7. Under Voltage Relay (UVR) Voltage Relay (UVR).
ELECTRICAL CONTROLS
Refer to pages 27 & 28 for A generation wiring FLS - Flow Switch. For ACDX/AUDX units, a
diagram. chilled water flow switch must be installed
The following electrical controls that are used on A while the package is in operation. Wire the
generation only are marked (A Gen). flow switch to the terminals shown on the
S1 - Power Switch (115V Control Circuit)
This switch energizes the control circuit and CWP - Chilled Water Pump Interlock.
must be left on (except for temporary For ACDX/AUDX units, it is recommended
control circuit service work) to allow normal that an interlock between the chilled water
on cycle operation. Compressor sump pump and the package be provided to
heaters are connected before this switch prevent the unit from operating with the
and are not affected by switch position. chilled water pump off. Connect the
S2 - Compressor Switch. This switch diagram.
S3 disconnects power from the corresponding
S4 compressor control circuit. This switch is S5 1PS - High Pressure Safety Switch (Manual
also used to reset the motor temperature (A Gen) Reset)
protector 1TAS). This is a manual reset switch that stops the
13
at the job site to ensure chilled water flow
wiring diagram.
interlock to the terminals shown on the
compressor in the event of excessive
discharge pressure. This is possibly
caused by fan failure or coil blockage.