Repairing The Cooling Circuit; Tightness Test; Hard Vacuum And Drying Of Cooling Circuit - Lennox Adnova THS Series Installation, Operating And Maintenance Manual

8.3

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.
8.4 Tightness test
Fill the circuit with anhydrous nitrogen supplied from a tank with a pressure-reducing valve until the pressure rises to 22
bar.
During the pressurization 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.
8.5

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
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.
@DNOVA THS_R410A-IOM-1304-E
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/h. If such a pump is available, one
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