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ENGLISH
ir33 +030220441 - rel. 2.0 - 01.05.2006
6.8 Pump down and low pressure
6.8.1 Enabling the function
The pump down function is activated by setting parameter c7 (pump down duration) to any value other
than zero.
The pump down valve must be connected to the auxiliary output, setting the relevant parameter (H1).
In addition, one of the digital inputs (A4, A5) must be set as a low pressure input.
6.8.2 Pump down function
When the set point is reached (if the minimum compressor ON time c3 has elapsed), the controller
closes the pump down valve, stopping the refrigerant gas on the compressor suction side.
Parameter c10 can be used to select pump down by pressure. In this case, once the pump down valve
closes, the compressor continues to operate until reaching the low pressure value or the time c7. When
this time elapses, the compressor is switched OFF, irrespective of the status of the low pressure input
and the Pd alarm (pump down ended by timeout) is disabled. In this case, the compressor autostart
function in pump down is disabl. Note: if the shut-down request occurs when the compressor is off and
the valve open (since, following the opening of the valve, the compressor has not yet started again),
the routine closes the valve and if necessary starts the pump down procedure if not in low pressure (if
autostart and pump down by pressure is enabled). When the controller requests the activation of the
compressor, if the minimum OFF time c2 and the minimum time between two starts of the compressor
c1 have elapsed, the pump down valve is opened, allowing the refrigerant gas to return to the
compressor intake. The compressor is started after the delay time c8 from the opening of the valve.
Note: if the start request occurs when the compressor is ON and the valve OFF (as it is in pump down
or autostart mode), the valve is opened immediately.
6.8.3 Compressor autostart in pump down
Parameter c9 is used to enable the compressor autostart function in pump down status. Once the
compressor has been stopped in pump down due to low pressure, if the low pressure switch signals an
increase in pressure, due to the faulty seal of the pump down valve, the compressor is started again until
it reaches the low pressure value.
The compressor autostart function considers the minimum OFF time c2 and the time between two
starts c1, while minimum ON time is ignored. Consequently, when reaching the low pressure value, the
compressor is stopped even if time c2 has not elapsed. The activation of a compressor autostart cycle
in pump down is signalled by the message AtS on automatic restoration of the next correct pump down
cycle.
6.8.4 Low pressure alarm (LP)
The low pressure alarm LP is activated when the pressure switch signals a low pressure situation with
the pump down valve open and the compressor operating. The low pressure alarm signal is nonetheless
delayed by the time set for parameter A7. Low pressure is not signalled during the compressor start-up
phase (opening of the pump down valve and subsequent activation of the compressor after the time
c8), during the shutdown of the compressor in pump down and during the compressor autostart cycle
in pump down. The low pressure alarm shuts off the pump down valve and the compressor, and is
automatically reset. The low pressure alarm can be reset in any situation.
Note: if control with two compressor steps is selected (with or without rotation, H1= 12 or 13) the pump
down is performed when both steps are deactivated.
The autostart function re-activates both steps.
6.9 Continuous cycle
Pressing S for more than 5 seconds activates the continuous cycle function, that is, the compressor
continues to operate, independently of the controller, for the time cc, so as to lower the temperature
even below the set point. If time cc is set to 0, the continuous cycle is never activated.
The continuous cycle is stopped after the time cc or when reaching the minimum specifi ed temperature,
corresponding to the minimum temperature alarm threshold (AL). If, after the end of the continuous
cycle, the temperature falls by inertia below the minimum temperature threshold, the low temperature
alarm signal can be ignored by suitably setting the alarm bypass delay time after continuous cycle, c6.
To start the continuous cycle, press S (MasterCella, powercompact and powercompact small) or
aux
+
def
(ir33, power and DIN) for more than 5 seconds.
The continuous cycle is not activated if:
• the duration of the continuous cycle (cc) is set to 0;
• the temperature is below the low level threshold;
• in reverse operation (heating), from parameter (r3) or from digital input (A4, A5),
• when the unit is OFF.
6.9.1 Await continuous cycle status
SThis status exists when the activation of the continuous cycle is requested, however it cannot be started
for one of the following reasons:
• compressor protection times (c1, c2, c3), as they delay activation of the compressor;
• immediate or delayed alarm from external dig. input (A4, A5), if this delays compressor activation;
• defrost, dripping or post-dripping in progress;
• compressor and fan start delay on start-up;
• door open (see Continuous cycle in progress, below);
• low pressure alarm (LP) active, as this delays activation of the compressor;
• high condenser temperature alarm (CHt) as this delays activation of the compressor.
During the continuous cycle request, the icon fl ashes.
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