Dunham-Bush ACDX, Installation, Operation And Maintenance Instructions

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ELECTRICAL CONTROLS (Cont'd)
12TAS - High Oil Temperature Switch (Manual This timer is used for incremental start
Reset) delay between Wye and Delta motor
This switch stops the compressor in the configurations. It is typically 5 seconds.
event of excessive oil temperature
(240
E
F). The bulb is mounted on the M - Contactor (Compressor and Fan Motor)
discharge line from the compressor. The contactor, operated by the control
MOL - Compressor Overload (Manual Reset) compressor and fan motors. Contactors
On 208/230V systems, a compressor are used either singly or in parallel pairs
starter with overload relay is used for for across-the-line and wye delta start.
overload protection. If the current draw of These devices are amp rated to handle
the compressor exceeds the trip point of both rated load amps and locked rotor
the overload, the compressor will be shut amps.
down.
9PS - Low Pressure Switch (Manual Reset, This contactor is used for generating the
(A Gen) Time Delay) Wye configuration of the motor windings
This is a switch which stops the at the start of a compressor.
compressor in the event of sustained low
suction pressure, possibly caused by
CR - Relays (Miscellaneous Control)
inadequate refrigerant flow, chiller water These relays provide the necessary
flow, or refrigerant loss-of-charge. It is circuit logic for lock-in, lock-out and
equipped with a 120 second time delay transfer functions.
(unless otherwise listed) to avoid
nuisance low pressure shutdown during
HTR - Crankcase Heater
transient conditions. Energized continuously as long as control
5TR Units with low ambient option have a 2 supplied with the unit) is closed and
3TAS minutes timer (5TR) that extends the low compressor is off. This heater maintains
(A Gen) pressure time delay to 4 minutes at the crankcase temperature above the system
start of the compressor. This only occurs temperature during the compressor off
when ambient temperature is below 40
E
F. cycle, preventing refrigerant migration in
(3TAS is measuring ambient temperature to the crankcase and consequent
and opens below 40
E
F). compressor damage.
10,11PS - Fan Pressure Switch (Automatic, Reverse Chiller Heater and Thermostat (ACDX
(A Gen) Acting) only)
This switch (in multiples) is used to stage The chiller heater with integral thermostat
condenser fans on and off to maintain is powered by a separate customer
adequate high side pressures for proper supplied 115VAC source. The heater
system operation by controlling net air turns on when the shell temperature
flow across the condenser coils (See Fan drops to 38
E
F. This helps prevent a
Cycling Control Section.) chiller freeze-up under low ambient
2TAS - Freeze Thermostat (Manual Reset)
(A Gen) This thermostat, sensing water 4TAS - Operating Thermostat
temperature leaving the cooler vessel, (A Gen) This microprocessor based temperature
provides chiller vessel protection against controller senses leaving chilled water
freeze-up if the leaving water temperature temperature and cycles the compressor
drops dangerously low. Normally set to on/off and loads/unloads the
open at 38
E
F, this thermostat setpoint can compressor(s) as the system load
be decreased for glycol systems as changes. The desired leaving water
required. temperature is set on the Setpoint dial
7TR - Fast Unload Timer initial control band setting should be 4
E
.
This timer provides a 30 second fast This may need to be increased if
unload signal at the start of a compressor. compressor cycling is observed.
The normal load/unload solenoids are de-
energized during this time delay.
SOL - Liquid Line Solenoid Valve
10TR - Wye-Delta Timer (Option)
circuit, provides power individually to the
C - Shorting Contactor (Wye-Delta Option)
circuit power disconnect switch (not
conditions.
using the "water" scale (10-60
E
F). The
Closes when the compressor(s) is off to
prevent any liquid refrigerant from
accumulating in the chiller during the off
cycle.
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