AEC ACOA Series Air-Cooled Central Chillers - Manual (Page 44)

6-12 Contactors - M
Contactors, operated by the control circuit, provide power individually to the compressor and fan
motors. Contactors are used either singly or in parallel pairs for across-the-line (simultaneous
operation) start. These devices are sized to handle rated load amps and locked rotor amps.
6-13 Relays - CR
These relays provide the necessary circuit logic for lock-in, lock-out, and transfer functions.
6-14 Crankcase Heater - HTR
The crankcase heater is continuously energized when main power is supplied to the chiller and
the compressor is off. It maintains crankcase temperature above the system temperature during
the Compressor Off cycle, preventing refrigerant migration into the crankcase and consequent
compressor damage.
6-15 Operating Thermostat - 4TAS
This thermostat senses From Process chilled water temperature and cycles the compressor
on/off or unloads a compressor as the system load changes. A two-stage device is used on single
compressor units with one stage of cylinder unloading. A four-stage device is used on single
compressor units with two stages of cylinder unloading and on two compressor units.
6-16 Liquid Line Solenoid Valve - SOL
This valve closes when the compressor(s) is/are off to prevent any liquid refrigerant from
accumulating in the chiller during the off cycle.
6-17 Unloading Solenoid Valve
This solenoid is energized to unload a cylinder bank on the compressor.
ACOA Series Air-Cooled Central Chillers
Page 43