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Pump down function
This function foresees problems in the compressor caused by movements of coolant, using a stop/start technique for
the installation, controlled via the liquid solenoid, the low pressure switch and the compressor itself.
This function is only available for InI 2, 5 and 7 and requires the connection of a low pressure switch in digital input
1 (I10=7).
STOP
When the temperature in sensor S1 reaches the set point (SP) value, the COOL relay deactivates, closing the solenoid
valve.
Because the compressor continues to operate, pressure in the evaporator quickly drops. Upon reaching a given value,
the low pressure switch activates, changing the status of digital input 1, which stops the compressor (AUX 1 relay).
This manoeuvre isolates all of the coolant in the high-pressure line, far from the compressor crankcase, preventing
serious faults upon start-up.
Should the low pressure switch fail, the controller stops the compressor once the safety interval defined in C20 has
elapsed, displaying the message “Pd” (an informative message that does not affect the unit's operation).
If C20 time is 0 (default value), the compressor will not stop until the low pressure switch is activated, but it will
display the “Pd” message after 15 minutes.
START
When the temperature in sensor S1 reaches the set point value plus the differential (SP+C1), the COOL relay acti-
vates, opening the liquid solenoid. This increases the pressure in the evaporator, deactivating the low pressure switch,
which turns the compressor on.
If, some time (determined by C19) after the liquid solenoid is opened (COOL relay set to ON), the low pressure
switch does not deactivate, the controller will once again close the solenoid (COOL relay set to OFF) 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 C19 time is 0 (default value), the solenoid will remain open until the low pressure switch deactivates, but it will
display the “LP” message after 5 minutes.
STAND-BY
If the pump down function is active, there may be a delay between starting the Stand-by function and the
controller stopping; this is because certain installation control phases cannot be interrupted.
To force the stop of the controller, press the Stand-by key again for 3 seconds.
Liquid
solenoid
Low pressure
switch
Pressure
switch fault
Pressure
switch fault
Compressor
Pressure in
evaporator
Summary of Contents for AKO-16526
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