4.Welding Soldering Brazing

Core Comparison Table

2. Soldering in RAC

Primarily used for electrical connections and low-pressure water lines.

• Filler Metal (Solder): Alloy of Tin (Sn) and Lead (Pb). Common ratio is 60:40.

• Flux: Typically Rosin-based (for electronics) or Zinc Chloride (for plumbing). It prevents oxidation during heating.

• Technique: Uses a soldering iron or a small butane torch.

• Fact for Exams: “Tinning” is the process of coating the soldering iron tip with a thin layer of solder to improve heat transfer.

3. Brazing: The Standard for RAC

90% of joints in a refrigeration circuit (compressor to condenser, evaporator to capillary) are brazed.

• Capillary Action: The ability of the molten filler to flow into narrow gaps regardless of gravity.

• Filler Materials:

  • Silver Brazing Alloy (Silver Solder): Contains 5% to 45% Silver. High strength, used for joining copper to steel/brass.

  • Phos-Copper: (Copper + Phosphorus). Used for Copper-to-Copper joints.

• Self-Fluxing: Phos-copper alloys are self-fluxing on copper. The phosphorus removes the copper oxide.

• Purging: While brazing, Dry Nitrogen must be bled through the pipe at low pressure (1-2 PSI) to prevent “Cupric Oxide” (black soot) from forming inside the pipe, which could clog the expansion valve.

4. Gas Welding (Oxy-Acetylene)

Standard heat source for brazing and light welding in RAC.

• The Equipment:

  • Oxygen Cylinder: Painted Black. (High pressure, ~2000 PSI).

  • Acetylene Cylinder: Painted Maroon/Red. (Dissolved in Acetone, ~250 PSI).

• Flame Types:

  • Neutral Flame: Equal Oxygen/Acetylene. Used for most welding.

  • Oxidizing Flame: Excess Oxygen. Used for welding brass/bronze.

  • Carburizing (Reducing) Flame: Excess Acetylene. Used for brazing and hard-facing.

5. Critical Safety & Knowledge (Exams Focus)

• Flashback Arrestor: A safety device fitted to the regulator/torch to stop a flame from traveling back into the cylinders.

• Cleaning: Joints must be mechanically cleaned (sandpaper/emery cloth) and chemically cleaned (flux) to ensure a proper bond.

• Direction of Heat: Always heat the thicker pipe or the female part of the joint first; the filler metal always flows toward the heat.

• Pressure Testing: After brazing, the system is tested with Nitrogen at high pressure to check for leaks using soap solution or electronic detectors.

Key Fact: In RAC, Silver Brazing is often incorrectly called “Silver Soldering,” but technically, since it happens above 450°C, it is always a Brazing process.