Installation - Operation - Maintenance manual (IOM) • AIR COOLED CHILLERS & SPLIT UNITS - 1106-E • 27 •
6.2.1.7 - Fan control pressure switch and thermostat:
The function of these devices is to ensure a level of head pressure compatible with proper unit operation.
An increase in outdoor air temperature increases head pressure, and this is maintained at its required value by fan
operation.
6.2.1.8 - Antifreeze function:
This function only exists on units designed for brine or glycol/water chilling for which the freezing temperature
depends on the concentration of the solution.
Whatever type of device is used (see case 1 and 2), cut-out by the antifreeze function causes immediate unit
stoppage.
CASE 1 : Antifreeze thermostat:
This device monitor chilled liquid temperature at the evaporator outlet. It triggers when the temperature goes below
the minimum value (+ 4°C for water).
CASE 2 : Antifreeze pressure switch:
This monitors evaporating pressure of the refrigerant. It triggers when the temperature goes below the preset
minimum value.
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.
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