HVAC/R System Installation: Soldering, Brazing, and Evacuation Methods

Posted on Oct 26, 2025 in Technology

Soft Soldering Techniques

Soft soldering is performed at temperatures between 190°C and 260°C, always below 500°C. The most commonly used filler materials are 50/50 tin/lead and 95/5 tin/antimony. The heat source for this type of joining is typically a butane gas torch.

Soft Soldering Operations

  1. Clean the junction thoroughly.
  2. Apply the flux to the male connection.
  3. Attach the connection piece to the tube.
  4. Heat the joint and apply solder.
  5. Dry and ensure the joint is very clean.

Brazing (Hard Soldering)

Brazing, also known as hard soldering, requires temperatures higher than soft soldering, typically using fusion temperatures above 500°C, depending on the filler metal used. The execution process is similar to soft soldering.

Filler metals are usually copper (Cu) alloys, often containing silver content ranging from 0% to 60%. Common heat sources include oxy-butane or oxy-acetylene torches.

Brazing Procedure

After cutting and deburring, the following steps should be performed:

  1. Clean the joint points.
  2. Place the connection piece onto the tube.
  3. Heat the joint and apply the filler metal and flux.
  4. Allow the joint to dry and clean it thoroughly.

Copper Pipe Types and Applications

Annealed (Soft) Copper Pipes

Used primarily for refrigeration and air conditioning (A/C) systems. These tubes come in rolls, typically 15 meters long, sealed and dehydrated. Their main quality is flexibility: they can be bent using tube benders or bending springs, and they are easily widened and flared. They are identified by their outer diameter, ranging from 1/4″ to 7/8″.

Rigid (Hard Drawn) Copper Pipes

For refrigeration and A/C, rigid pipes are presented in straight bars, typically 5 meters long, with sealed and dehydrated ends. They are identified by their outside diameter, ranging from 3/8″ to 3 5/8″.

For standard water and heating installations, rigid pipes are presented in bars 5 to 6.10 meters long. In this case, they are designated by their internal diameter in millimeters (e.g., 15mm, 18mm, 20mm).

Copper Tube Expansion Techniques

Tube expansion is the process of joining two pieces of copper pipe of the same diameter by expanding and flaring the end of one piece to dock with the other. This union is typically secured using soft or hard solder.

Expansion can be achieved using several methods:

  1. Using a punch that is struck with a hammer-type tool.
  2. Using a lever-type expansion tool.
  3. Using a specialized flaring and widening toolkit.

Refrigeration System Leak Detection

The best procedure for leak detection involves constant and stabilized pressure testing, using a pressure source that does not change significantly due to temperature variations. Nitrogen is excellent for this pressure test.

Warning: Never use oxygen or compressed air to carry out this test.

The standard procedure is to load the system with a small amount of refrigerant (e.g., 0.70 kg/cm²) and then add nitrogen to reach the required test pressure (e.g., 10.5 kg/cm²). The small amount of refrigerant that escapes will be sufficient to be detected by specialized leak detection equipment.

Vacuum Theory in HVAC Systems

Achieving a vacuum means lowering the system pressure below atmospheric pressure. Atmospheric pressure exerts a force equivalent to:

  • 1.03 kg/cm² (approx. 1 atmosphere)
  • 29.92 inches of mercury (inHg)
  • 760 mm of mercury (mmHg)

To properly evacuate a cooling system, the pressure must be reduced to approximately -1 kg/cm² (29.92 inHg vacuum) to expel all non-condensable gases and moisture. This state approaches a perfect vacuum, though a true perfect vacuum is impossible to achieve in practice.

Vacuum measurement is typically performed using the low-pressure gauge on a manifold set, which features a scale calibrated in inches of mercury (inHg) below the 0 bar indication.

Manifold Gauge Set Functions

The manifold gauge set is a crucial tool used for several system operations:

  1. Measuring Pressure:
    • Low-pressure side: Measures system pressure (valve typically closed during operation).
  2. Charging Refrigerant:
    • Charging liquid refrigerant: Low side open, High side closed.
    • Charging gaseous refrigerant: High side open, Low side closed.
  3. Vacuum Pumping (Evacuation):
    • Both High and Low pressure valves must be open to the vacuum pump.