Rivacold MX Betriebs- Und Wartungsanleitung Seite 15

5. 4 Oil return
All systems must be designed so as to ensure oil return to the compressor.
In the situation shown in Drawing 3 (condensing unit placed above the evaporator), it is important to fit
siphons along the suction line every 2 m of difference in height so as to guarantee oil return to the
compressor. In any case, along horizontal stretches it is important for the suction line to have a slope
of at least 3% towards the compressor.
5. 5 Adding oil
In the majority of installations where all piping is no longer than 10 m, it is not necessary to add oil.
However, when the pipes are oversized compared to standard conditions or they are longer than 10m,
a small quantity of oil must be added.
5. 6 Vacuum
For the correct operation of the refrigerating equipment and the duration of the compressor, it is very
important for the vacuum in the system to be set correctly. This will ensure that air and above all,
humidity contents are below the permitted values. The introduction of new gas types has meant the use
of new polyester-type oils that have high-level hygroscopic characteristics and which require more
attention when setting the vacuum. We would advise setting the vacuum on both sides of the circuit. In
any case, the target value is a pressure no higher than 5 Pa.
Important: in order to avoid irreparable damage to the compressor, never start it in vacuum conditions and without
.
the gas charge
During the vacuum and charge procedure, remember to energise the solenoid valve coil of the liquid
line
5. 7 Refrigerant charge
After the vacuum-setting operation, the system must be charged with the type of refrigerant stated on
the label or with one of the alternative types allowed. To charge the refrigerant correctly, we
recommend that, after setting the vacuum, you pump part of the refrigerant into the compressor to
"break the vacuum". Then start the compressor so that it sucks up the residual part of the refrigerant.
For the correct calculation of the gas charge, connect gauges to the pressure inlets (already fitted).
Pressure values must be compatible with the operating conditions of the machines.
mixtures of refrigerating gas must be charged into the system in their liquid state only.
Important:
Charging operations must be carried out by specialised technicians only.
For charging, recovering or checking the refrigerant, use gloves to protect against low temperatures.
5. 8 Leakage checks
A system can operate correctly over time and for the entire duration of the compressor only if all
instructions for a correct installation are followed. These include the absence of refrigerant leaks. It
has been estimated that leaks of 10% of the refrigerant charge during 15 years of compressor
operation still guarantee a good level of operation of the refrigerating system. With the new types of
gas (R134a, R404a and mixtures) the possibilities of refrigerant leaks through welding or connections
that have not been carried out correctly increase because of the reduced molecular dimensions of
these gas. For these reasons, it is very important that welding is checked for leakage using methods
and equipment that are suitable for the type of refrigerant in use.
5. 9 Crankcase heater (supplied)
Whenever the compressor operates in ambient temperatures of less than +5°C, it is compulsory to use
a crankcase heater in order to avoid the build-up of liquid in the lower side of the compressor during
stoppages. Furthermore, it is necessary to choke the condenser, for example, by reducing its air
capacity (i.e.: by means of a speed regulator)..
5. 10 Operating cycles
• The system has to be sized so as not to have more than 5 on/off cycles per hour.
• The intervention of the Thermal/Amperometric protection device switches off the compressor, which
will be started again after the time required for the protection device contacts to be connected.
5. 11 Operating times
• The systems must be sized for max. 80% of standard compressor operation.
• 100% compressor operation only occurs in special overload and ambient temperature conditions
that are outside of the normal permitted operating limits.
MX SX Pag. 15 REV. 14 11/05
UK