Cooling
14
12. Pressure testing
Pressure leak test
Both condenser and evaporator units have been strength & leak tested, dehydrated and filled with a holding charge of “dry air”
during manufacture. After installation, the entire system should be leak tested before evacuation as follows:
• Pressurize the high-pressure side of the system with Nitrogen to the maximum R448A HP pressure of 25 barg.
CAUTION:
A PRV (set pressure of 27.5 Barg) is fitted and if over pressurized this will blow and will need replacement*
• Check the whole system for leaks, if a leak is found, release the test pressure and repair the leak, then repeat test from the
start.
*Warning: wear safety goggles when performing the leak testing, and ensure all unnecessary personnel are excluded
from the area*
*Warning: when leak testing with nitrogen, ensure that appropriate procedures and effective nitrogen detection precautions
are in place to prevent asphyxiation if nitrogen is released *
13. Evacuation
The entire system should be evacuated prior to charging as follows:
• Connect a gauge manifold to the 1/4” flare connections on each service valve. Check the service valves are fully back
seated to ensure the pipe and service connection is fully open.
• Connect a vacuum pump to the service port on the gauge manifold, and ensure all paths are open.
• Evacuate the system to below 225 microns (0.3 mbar). The pump should be isolated, and the system pressure monitored.
A rapid continuous rise in pressure would indicate a leak in the system.
• During the evacuation process, the crankcase heater should be turned on, by energizing the power supply to the unit.
*Warning: do not megger test or start the compressor whilst under a vacuum*
14. Refrigerant charging
It is good practice to charge the system immediately after evacuation. This system is designed for use with R448A as the
refrigerant and should only be used with R448A. As R448A is a blend, the system MUST always be charged with liquid and
never as a gas. While the unit is under vacuum, liquid can be charged into the liquid line via the Schrader point. The main
charging process should be completed during commissioning.
Depending on ambient conditions, it may not be possible to fully charge the system from vacuum. If necessary, additional charge
can be added whilst running the system close to normal operating conditions (as shown in the table below). The remaining charge
is added via the suction service Schroeder. The refrigerant must be added as a liquid to maintain the R448A composition, but no
liquid should be present in the suction line of the, compressor. Therefore, an additional pressure drop is required to ensure that
the liquid flashes into gas. This is achieved using a liquid expansion charging device, connected via a gauge set.
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