1569H042 Ed.03
17
9.5.- 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 feature to be active, the auxiliary relay must be set as "Pump down" (
P6=1
).
SHUTOFF
When temperature probe 1 reaches the set point value (
SP
), the AUX 1 relay is deactivated by closing the liquid
solenoid.
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.
DOES NOT
activate the alarm relay or the sound alarm, it is only shown on the display.
STARTUP
When temperature probe 1 reaches the set point value plus the differential (
SP+C1
), the AUX 1 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.
If a period of time has elapsed (determined by
P14
) after the liquid solenoid is opened (AUX 1 relay set to ON), the
low pressostat will not be deactivated, the controller will once again close the solenoid (AUX 1 relay set to OFF)
and the “
LP
” message will be displayed. This manoeuvre will be repeated every 2 minutes indefinitely until the
pressostat is deactivated and the installation reverts to its normal operation.
If time
P14
is 0 (default value), the solenoid will stay open until the low pressostat is deactivated, but it will display
the “
LP
” message after 3 minutes.
DOES NOT
activate the alarm relay or the sound alarm, it is only shown on the display.
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 1
Digital
Input
COMP.
Time
SP
SP
SP+C1
SP+C1
