1763H532 Ed.02
7.5.- Pump down function
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 function to be active, it must be configured in parameter
P26= 1.
PARO
When the temperature in probe 1 reaches the set point (
SP
) value, the liquid solenoid closes.
Since the compressor is still running 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.
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 "
Pd
", but it will continue to function normally. (informative message, does not affect the equipment
operation).
If time
P15
is 0 (default value), the compressor will not stop until the low pressostat is activated, but it will display
the “
Pd
” message after 15 minutes.
STARTUP
When the temperature in probe 1 reaches the set point plus the differential (
SP
+
C1
) value, the liquid solenoid
opens. This increases the pressure in the evaporator, deactivating the low pressure switch, which turns the
compressor on.
If a period of time (determined by
P14
) has elapsed after the liquid solenoid is opened, the low pressure switch
will not be deactivated, the controller will once again close the solenoid, and the “
LP
” message will be displayed.
This manoeuvre will be repeated every 2 minutes, indefinitely, until the pressure switch is deactivated and the
installation reverts to its normal operation.
If the time for
P14
is 0 (default value), the solenoid will stay open until the low pressure switch is deactivated, but
after 3 minutes it will display the “
LP
” message.
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
SOLEN.
Digital
Input
COMP.
Time
SP
SP
SP+C1
SP+C1
13
