5 PIPING
WARNING! Risk of explosive discharge from high-pressure refrigerant. Can cause equipment
damage, injury or death.
Relieve pressure before working with or cutting into piping.
WARNING! Risk of refrigerant system rupture or explosion from overpressurization. Can cause
equipment damage, injury or death.
Local building and plumbing codes may require that a fusible plug or other type of pressure
relief device be installed in the system. Do not install a shutoff valve between the compressor
and the field-installed relief device.
Consult local building and plumbing codes for installation requirements of additional pressure
relief devices when isolation valves are installed as shown in Figure 5.1 on page55. Do not
isolate any refrigerant circuits from over-pressurization protection.
NOTE: POE (polyol ester) oil, required with R-407C/R-410A and used with some R-22 systems, is much
more hygroscopic than mineral oils. This means that POE oil absorbs water at a much faster rate when
exposed to air than previously used mineral oils. Because water is the enemy of a reliable refrigeration
system, extreme care must be used when opening systems during installation or service. If water is
absorbed into the POE oil, it will not be easily removed and will not be removed through the normal
evacuation process. If the oil is too wet, it may require an oil change. POE oils also have a property that
makes them act as a solvent in a refrigeration system. Maintaining system cleanliness is extremely
important because the oil will tend to bring any foreign matter back to the compressor or plug the
microchannel coil. Always use a flow of dry nitrogen when brazing.
5.1 Piping Guidelines
Indoor units and condensers both ship with holding charges of inert gas. Do not vent the condenser until
all refrigerant piping is in place, ready for connection to indoor unit and condenser.
• Use copper piping with a brazing alloy with a minimum temperature of 1350°F (732°C), such as
Sil-Fos. Avoid soft solders such as 50/50 or 95/5.
• Use a flow of dry nitrogen through the piping during brazing to prevent formation of copper
oxide scale inside the piping. When copper is heated in the presence of air, copper oxide forms.
POE oil will dissolve these oxides from inside the copper pipes and deposit them throughout
the system, clogging filter driers and affecting other system components.
• A pure dry nitrogen flow of 1-3 ft
3
/min (0.5-1.5 l/s) inside the pipe during brazing is sufficient to
displace the air. Control the flow using a suitable metering device.
• Ensure that the tubing surfaces to be brazed are clean and that the ends of the tubes have
been carefully reamed to remove any burrs.
• Ensure that all loose material has been cleaned from inside the tubing before brazing.
• Protect all refrigerant line components within 18" (460mm) of the brazing site by wrapping
them with wet cloth or suitable heat sink compound.
• Isolate piping from building using vibration isolating supports.
Vertiv | Liebert® MC™ Installer/User Guide | 53
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