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Desert Aire - SP Manual
ensure that the flux is not introduced to the inside of the tube. It is recommended
that phosphorous bearing alloys be considered for copper to copper connections
due to their self-fluxing on copper to copper joints. Refer to alloy manufacturer’s
guidelines for details on compatibility.
• Flow nitrogen into tubing to prevent the formation of copper oxides.
- Copper oxides form rapidly when copper is heated to temperatures required by
the brazing process and exposed to oxygen in the air. Copper oxides flake
easily on the inside of the tubing and dislodge easily when the system is filled
with refrigerant and oil. The particulate can move throughout the system and
cause contamination on valves and other critical components. System filters may
become fouled.
- Flowing nitrogen into the system and ensuring that the inside of the tube is
significantly free from oxygen while brazing ensures that oxides do not form. As
the last joints of a system are made, additional thought must be made on the
location where the nitrogen can escape. Schrader valves are placed throughout
the system. These valves can be opened to allow for nitrogen to flow without
generating pressure behind the braze joint that is being created.
• See section 5.1.1 for special procedures related to compressor replacements
• Replace liquid line filter dryer as last step in system repair. Note that the dryer will readily
absorb moisture from the ambient air and must be open only for as long as required for
installation.
• After completion of all repairs, pressure test system using nitrogen pressure decay test or
nitrogen with tracer gas and appropriate leak detector.
Evacuation
• Carefully inspect pump and related equipment before connecting to system. Ensuring
gaskets are in good condition and pump is capable of low vacuum levels can save time.
Connect pump(s) to as many locations as possible ensuring all locations are well sealed.
If a field charge will be required, connecting a refrigerant tank to the system with a good
valve is recommended. Any hose connections requiring purging of non-condensable can
be done at this point.
• Evacuate the line to 400 microns measure at a point on the system furthest away from
the pump.
- Note that a gauge installed on the pump or in close proximity will give a lower
reading while the unit is being evacuated.
- A deep vacuum gauge should be used to evaluate the pressure. Compound
manifold gauges do not allow for enough accuracy at the pressures required.
- The system should be able to hold a vacuum under 500 microns for more than 10
minutes.
- If pressure continuously rises at a rapid rate there is likely a system leak. Review
all piping connections and correct before continuing evacuation.
- Pressure rising above 500 microns and tending to stabilize at a higher pressure
indicates the system has moisture above specifications. Continue evacuation until
500 microns or lower can be held for a minimum of 10 minutes.
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