AEC ACOA Series Air-Cooled Central Chillers - Manual (Page 43)

6-7 Compressor Oil Failure Switch - 3PS
Manual Reset, Time Delay
This differential pressure switch continuously compares oil pressure with suction pressure to
provide protection against low net oil pressure. It has a two (2) -minute delay to avoid nuisance
shutdowns due to momentary low fluctuations of oil pressure due to oil foaming, etc.
6-8 Low Pressure Switch - 9PS, 5TR, 3TAS
Manual Reset, Time Delay
This switch stops the compressor in the event of sustained low suction pressure, possibly caused
by inadequate refrigerant flow, chilled water flow, fan failure, coil blockage, or refrigerant loss
of charge. It has a two (2) -minute delay to avoid nuisance shutdowns during transient
conditions.
Low ambient option ACOA units have a two (2) -minute timer (
5TR ) that extends the low
pressure time delay to four (4) minutes at the start of the compressor. This only occurs when the
3TAS thermostat senses ambient temperature below 40ºF (4ºC).
6-9 Fan Pressure Switch - 10PS, 11PS
Auto, Reverse Acting
This switch (in multiple) stages condenser fans on and off to maintain adequate high side
pressures for proper system operation by controlling net air flow across the condenser coils. See
Figure 20 on Page 39 for more information.
6-10 Compressor Cycle Timer - 1TR
This timer prevents rapid compressor recycling by providing a five (5) -minute compressor lock-
out immediately after any shutdown. The 12 restarts-per-hour limit protects the compressor
motor and bearings.
6-11 Timer - 4TR
This timer, used on multi-compressor units, provides staggered compressor starting. This feature
lets you avoid simultaneous compressor starts which can over-tax the main power supply.
Page 42
ACOA Series Air-Cooled Central Chillers