20
IOM / @DNOVA_THS-0508
e. Repairing the cooling circuit
Warning: while performing repairs on the cooling circuit or maintenance work on
the compressors, make sure the circuit is left open for as little time as possible.
Even if briefly exposed to air, ester oils tend to absorb large amounts of humidity,
which results in the formation of weak acids.
If the cooling circuit has undergone any repairs, the following operations must be carried out:
-
tightness test;
-
evacuation and drying of the cooling circuit;
-
charging with refrigerant.
If the system has to be drained, always recover the refrigerant present in the circuit
using suitable equipment; the refrigerant should be handled exclusively in the
liquid phase.
f.
Tightness test
Fill the circuit with anhydrous nitrogen supplied from a tank with a pressure-reducing valve until the
pressure rises to 22 bars.
During the pressurisation phase, do not exceed a pressure of 22 bars on the
compressor low pressure side
The presence of any leaks must be determined using special leak detectors. Should any leaks be
detected during the test, empty out the circuit before repairing the leaks with suitable alloys.
Do not use oxygen in the place of nitrogen as a test agent, since this would cause
a risk of explosion.
g. Hard vacuum and drying of cooling circuit
To achieve a hard vacuum in the cooling circuit it is necessary to use a pump capable of generating a
high degree of vacuum, i.e. 150 Pa of absolute pressure with a capacity of approximately 10 m
3
/h. If such
a pump is available, one evacuation will normally suffice to achieve an absolute pressure of 150 Pa.
If there is no such vacuum pump available, or whenever the circuit has remained open for long periods of
time, you are strongly recommended to adopt the triple evacuation method. This method is also
recommended when there is a presence of humidity within the circuit.
The vacuum pump should be connected to the inlets.
The procedure to be carried out is as follows:
- Evacuate the circuit until you reach an absolute pressure of at least 350 Pa: at this point inject nitrogen
into the circuit until you reach a relative pressure of about 1 bar.
- Repeat the step described above.
- Carry out the step described above for the third time, but in this case attempting to reach the hardest
vacuum possible.
Using this procedure you can easily remove up to 99% of pollutants.