EVCO S.p.A.
c-pro 3 nano CHIL | Application manual ver. 1.0 | Code 144CP3NCHE104
page 67 of 90
If with the machine on and when there is a cold request from the control, low pressure is detected, compressor start-up is inhibited and
the Low-pressure start alarm AL21 (and AL22 for Circuit # 2) is shown. The purpose of this condition is to inhibit compressor start-up
when there isn’t any Freon® gas in the circuit (there could be a coolant leak from the pipes).
8.17.4 Low pressure transducer alarm management (heat pump mode)
If the supply of pressure drops below a certain threshold, a low-pressure alarm AL41 (and AL42 for Circuit # 2) is generated. The
alarm causes the immediate arrest of the coolant circuit, also switching off any compressor that might be on and keeping the others
from starting up.
Upon start-up of the first compressor, the alarm is delayed for a certain interval to allow the compressors to take the coolant circuit to
maximum pressure.
At first the alarm is the autoresetting type, unless it exceeds a certain number of events in an hour (PA14), circumstance in which it
switches to manual reset; it can be reset if in the meantime the pressure has increased to a certain differential value over the minimum
threshold.
PA11 = Low pressure alarm set point
PA12 = Low pressure alarm differential
PA13 = Low-pressure alarm bypass period
PA14 = Maximum number of autoresetting low-pressure alarms
In the presence of low external air temperatures, the supply of pressure could drop below the minimum pressure threshold, thus
stopping compressor start-up. In such circumstances, you can activate a control that moves the alarm control threshold to a higher
value for a certain interval of time from start-up of the first compressor, however leaving all the protection devices and controls
preliminary to start-up in place.
PA16 = Enable low pressure control with low external temperature
PA17 = Low pressure alarm setpoint at low external temperature
PA18 = Low pressure alarm differential at low external temperature
PA19 = Low pressure alarm duration at low external temperature
This control can be enabled only in heat pump operating mode.
8.17.5 Low pressure start alarm
In the condition of low pressure (pressure switch or induced by transducer) or when it’s impossible to activate the compressors by its
request, a Low-pressure start alarm AL51 (and AL52 for Circuit # 2) activates. This is an autoresetting alarm and therefore it should
disappear, unless there is a Freon® gas leak from the circuit.
When the compressor is switched off after a low-pressure alarm, this alarm is delayed for a certain time interval PA20 to allow the
coolant circuit to enable compressor start-up.
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