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DEFROST
The defrost cycle is only active when the unit is operating as a heat pump. Its function is to prevent the formation of ice on
the surface of the exchanger (coil). Defrosting occurs based on the evaporation temperature measured by the probe BT3
located on the air-cooled coil. Various parameters set by the manufacturer optimise the operation of this function. The
operation of the defrost function is summarised in figures A and B. When the temperature measured by the probe BT3 falls
below the parameter START DEFROST SET POINT, a time starts counting (25min.). If the temperature measured by the
probe does not exceed the START DEFROST value during this time, the defrost cycle starts.
Figure A shows that the start of the defrost involves the stopping of the compressor and the reversal of the cycle, using the
4-way valve, for a period defined by the parameter d06, and then the restart of the compressor after a time equal to the
value set for the parameter d06. The CLIVET units are shipped with the parameter d06 set to 0, and consequently the
compressor is always on. During the defrost phase, the fans are off. The defrost will end when the temperature measured by
BT3 reaches the value set for the parameter d04 (18°C), or alternatively when the parameter d05 is exceeded (maximum
defrost time, 5min.).
Figure A
Figure B highlights another parameter, d07 (dripping time), which acts at the end of the defrost. Its function is to allow a
certain time (15sec.) to elapse before the reversing valve is activated and compressor starts again, and consequently the
unit starts operating as a heat pump. The fans also start operating again. During the defrost cycle, the compressor safety
times are ignored. When the 4-way valve switches, the low pressure alarm is bypassed for the time defined by parameter
A01 (120sec).
Figura B
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