Installation - Operation - Maintenance manual (IOM) • AIR COOLED CHILLERS & SPLIT UNITS - 0105-E • 27 •
Note: On units fitted with CLIMATIC control, see the appropriate user manual for more specific details.
6.2.1.9 - Differential oil pressure safety switch : (only on units with semi-hermetic compressors)
a) Reciprocating compressors:
This pressure switch initiates unconditional unit stoppage if differential oil pressure drops for more than two minutes
below a pre-established minimum safety value.
Differential oil pressure is the difference between the oil pump discharge pressure and the gas pressure inside the
compressor crankcase (suction pressure). The differential oil pressure safety switch is factory set and is not
modifiable on site.
b) Screw compressors:
This pressure switch initiates unconditional unit stoppage if differential oil pressure rises above a preset safety
value.
Differential oil pressure in this case is high pressure less the compressor oil injection pressure.
6.2.2 - Functions of electrical components
6.2.2.1 - Electronic or cam type anti-short cycle relay:
This device limits the number of compressor start ups.
Compressor motor thermal protection:
This device stops the motor if winding temperature rises too high and enables it to start up again when temperature
drops back to a normal value.
6.2.2.2 - Fan over current protection:
Circuit breaker designed to stop the fan motors in the event of phase over current in relation to the permitted value.
6.2.2.3 - Compressor motor over current protection:
Circuit breaker designed to protect each motor winding against accidental over current.
6.2.2.4 - Indicator lights:
The electrical control box is fitted with indicator lights enabling visualisation of the state of operation or non operation
of a function or given circuit.
There is also an indicator to show that the unit is powered up, an emergency stoppage indicator for each
compressor, an indicator to show stoppage of the compressor via the regulating system (through the main control
thermostat which is sensitive to chilled water temperature), a run light per compressor, and a general fan default
stoppage indicator (on air cooled units).
On units with CLIMATIC control, see the appropriate manual.
6.2.2.5 - Time delay relay for starting compressor motors one winding at a time (option) :
This optional relay is supplied on units ordered with the part winding start system. The time delay between starting
the first winding and the second winding cannot exceed 0.8 seconds.
6.2.2.6 - Chilled liquid pump interlock:
This interlock is made only if the the pump is supplied with the liquid chiller. As soon as the unit is powered up and
the remote on/off for the unit is validated, the pump starts running. Prior operation of the pumps is mandatory for
compressor operation.
Note : on units with CLIMATIC control, control of 1 or 2 water pumps is catered for by the control program.
6.2.2.7 - Flow switch for the chilled liquid (option) :
This control device initiates unconditional unit stoppage as soon as the flow of chilled liquid (water, brine, etc...)
ensured by the pump becomes insufficient, since this could cause rapid evaporator freeze up. When the contact
opens due to a lack of flow the unit must stop immediately.
If the purchaser installs a flow switch himself, electrical connections should be made to the two remote interlock
terminals (dry contact).
OPERATION
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