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English
Control
6.2 Protection and Safety Equipment
Defrosting System
(only for VLH models)
The VLH units are provided with an automatic de-
frosting system, which prevents the formation of ex-
cessive ice banks on coolant/air exchangers during
heat pump operation.
This system, which is part of the electronic control
system, is of the time/temperature type, and when
the temperature detected by a sensor at the inlet of
the coil drops below 0°C, once the preset time is
over, switches from heating to cooling the operation
of the unit, with the fans stopped.
During the defrosting cycle the compressor works
normally, but the coil’s fans remain off. The defrost-
ing cycle stops after the coil has been defrosted, and
at this point the unit can work in heating mode
again.
Both circuits are defrosted at the same time.
For safety purposes, fans are started also
during defrosting, if the discharge pressure
reaches considerable values.
Frost Protection for the Chilled Fluid
These units are provided with frost protection for the
chilled fluid. This protection consists of an electrical
resistor positioned in contact with the coolant/circu-
lating fluid exchanger, which is activated (although
the unit is off) when the temperature of the fluid drops
below 5 °C - the standard value for a non-glycol unit.
If the leaving water temperature drops below 4 °C
(standard value for a non-glycol unit) the machine’s
antifreeze alarm is activated. If the circulating fluid is
water, before the beginning of the cold season it is
advisable to drain the circuit to prevent water frost-
ing.
If the circuit cannot be drained, it is essential to
avoid de-energizing the unit, so as to permit the acti-
vation, when necessary, of the frost protection.
Compressor Protection
Compressors are equipped with a heating element
to prevent oil dilution, which may result in remark-
able risks of failure of compressors.
The windings of the compressors’ motors are provid-
ed with a thermal protection.
For VLS/VLH models an accessory kit for thermal
protection is available, for any overcurrent of scroll
compressors, which shall be shop-mounted.
Electrical flow switch
To ensure the correct operation of the unit, a electri-
cal flow switch must be installed, to prevent the unit
working in case of insufficient circulation of the
chilled fluid.
The electrical flow switch must be carefully
installed, according to the instructions given
by the Manufacturer.
The electrical flow switch must be installed on the
pressing side of the circulation pump for the fluid,
just upstream of the heat exchanger’s inlet. The elec-
trical flow switch must be installed in a horizontal
straight length of piping, in a position reasonably far
(both upstream and downstream) from localized
pressure drops (curves, valves etc.).
Continuous Regulation of the Fan Speed
When working in cooling mode, the standard unit
can reach a temperature of -5°C. The fans' speed
regulator, if installed, allows the unit to work at a
room temperature down to -18°C.
Differential pressure switch
This pressure switch halts the operation of the unit in
the event that it does not detect a sufficient pressure
drop through the exchanger.
Manuale VLS-VLH1 17-06-2005 9:05 Pagina 25
