ON
SP + DIF
Liquid
solenoid
Temperature
Low pressure
controller
Fault in pressure
controller
Fault in pressure
controller
Low Pressure
Alarm
Compressor
Pressure in
evaporator
ON
ON
+
Pump
down
duration
Pump down
ON delay
OFF
SP
OFF
OFF
AUX
Entrada
digital
COMP.
Time
SP
SP
SP+DIF.
SP+DIF.
18
8.5.- Pump down function
This function foresees problems in the compressor caused by movements of coolant, using a stop/start technique of the
installation, controlled via the liquid solenoid, the low pressure controller and the compressor itself.
The auxiliary relay must be configured as "Pump down control", the liquid solenoid must be connected to the 40 and 41
terminals and there must be a low pressure controller connected as indicated in the diagrams (See page 7).
STOP
When the temperature in probe 1 reaches the set point (SP) value, the liquid solenoid closes.
Due to the compressor continuing to operate (COMP. relay ON), the pressure drops quickly in the evaporator, and
therefore activates the low pressure controller and the compressor stops.
If during this process the low pressure controller does not detect the change of pressure, the controller will stop after the
safety time defined in
Pump down duration
.
START
When the temperature in probe 1 reaches the set point value plus the differential, the liquid solenoid opens, making the
pressure in the evaporator increase and deactivating the low pressure controller, which will start the compressor up.
When a balance is reached between the high and low pressure before the start up, this is much gentler and lengthens
the life of the compressor.
If after a time after opening the liquid solenoid the low pressure controller does not deactivate, the controller closes the
solenoid again and activates the low pressure alarm. This time is defined using the
Pump down On delay
parameter.
STAND-BY WITH PUMP DOWN
If the pump down function is active and the compressor is operating, when the Stand-by function starts the unit stops
the compressor in a controlled manner as explained in the "STOP" section and displays on the screen the "Pump
down" message, and when it has finished, it automatically goes to the Stand-by mode.
