4.5.- Pump down function
(only four-relay controllers)
This function prevents compressor problems caused by movement of the refrigerant, using a stop/start technique of
the unit controlled by liquid solenoid, the low pressure switch and the compressor.
For this feature to be active, the auxiliary relay must be set as "Pump down" (P6=4), which automatically
configures digital input 1 as "low pressure switch" (P10=7)
SHUTOFF
When temperature probe 1 reaches the set point value (SP), the AUX relay is deactivated (OFF) by closing the liquid
solenoid.
Since the compressor is still running (COOL relay ON) the evaporator pressure drops suddenly. When it reaches a
specific point, the low pressure switch is activated, changing the state of digital input 1, and the controller stops
the compressor (COOL Relay OFF).
This manoeuvre isolates the refrigerant from the compressor crankcase, preventing serious damage on start-up.
In case of low pressure switch failure, the controller stops the compressor after the safety time set at P15, showing
the message "Art", but it will continue to function normally.
STARTUP
When temperature probe 1 reaches the set point value plus the differential (SP+C1), the AUX relay is activated
(ON), opening the liquid solenoid. This causes the pressure in the evaporator to increase, disabling the low pressure
switch. The controller detects this change and starts the compressor (COOL relay ON).
Balancing the high and low pressure settings before start-up makes it much smoother and extends compressor life.
If after a time (as determined by P14) after opening the liquid solenoid (AUX relay ON), the low pressure switch is
not turned off, the controller will again close the solenoid (AUX relay OFF) and will repeat the manoeuvre after 2
minutes. The controller will display "Art".
STAND-BY
If the pump-down function is active, some time may elapse from the time the stand-by function starts until the
controller stops. This is because certain control phases of the system cannot be stopped.
ON
Liquid
solenoid
Low pressure
switch
Pressure
switch fault
Pressure
switch fault
Compressor
Evaporator
pressure
ON
ON
+
P15
P14
OFF
OFF
OFF
AUX
Digital
Input
COOL
Time
SP
SP
SP+C1
SP+C1
16
