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Unit 2 — Introduction to Refrigerants & Handling Practices
Section 1 — Refrigerants, Gases and Oils

1.3 Types of Gases in HVAC

Characteristics, uses, and safety requirements for the gases commonly encountered in refrigeration and air conditioning work.

1.3.1 — Gases at a Glance

Refrigeration and air conditioning technicians work with several gases beyond refrigerants. Each has a specific purpose and a distinct set of hazards. Knowing the properties of each gas — before handling — is essential for safe and effective work.

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Acetylene

Highly flammable. Used for oxy-acetylene brazing and cutting of copper tubing. Stored dissolved in acetone — cylinders must remain upright.

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Argon

Inert. Used as a welding shielding gas (TIG/MIG) to prevent oxidation. Non-flammable but can displace oxygen in confined spaces.

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Carbon Dioxide

Non-flammable. Used as refrigerant R-744 and for purging. High-pressure cylinders require careful handling; risk of asphyxiation at high concentrations.

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Helium

Inert. The preferred gas for precision electronic leak detection due to its small molecular size and fast diffusion rate.

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Nitrogen

Dry and inert. Used for pressure testing, purging lines during brazing, and breaking vacuum. Requires regulators and gauges rated for the intended pressure.

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Oxygen

Vigorously supports combustion. Used with acetylene for oxy-fuel work only. Must never be used for pressure testing or purging refrigeration systems.

1.3.2 — Gas Profiles

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Acetylene

Acetylene is a highly flammable gas used primarily for oxy-acetylene brazing and cutting.

  • Provides a very high flame temperature when combined with oxygen — suitable for brazing copper tubing in refrigeration work.
  • Stored dissolved in acetone within specially designed cylinders.
  • Cylinders must be kept upright and away from heat and ignition sources.
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Argon

Argon is an inert gas used for shielding in welding and in some leak-testing applications.

  • Provides a protective atmosphere in TIG and MIG welding to prevent oxidation of the weld.
  • Non-reactive and non-flammable but can displace oxygen in confined spaces.
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Carbon Dioxide (CO₂)

Carbon dioxide is used both as a refrigerant (R-744) and as a testing or purging gas.

  • High-pressure cylinders require careful handling.
  • CO₂ is non-flammable but can cause asphyxiation in high concentrations.
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Helium

Helium is a very light, inert gas used in precise leak-testing applications.

  • Helium molecules are small and diffuse quickly — ideal for sensitive electronic leak detection.
  • Used in combination with mass spectrometer leak detectors for extremely low leak rate testing.
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Nitrogen

Most Common

Nitrogen is a dry, inert gas commonly used in refrigeration and air conditioning work.

  • Used for pressure testing, purging lines during brazing, and breaking vacuum after evacuation when required.
  • Cylinders must be used with appropriate regulators and gauges rated for the intended pressure.
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Oxygen

Oxygen is used with acetylene or other fuels for oxy-fuel brazing and cutting.

  • Supports combustion vigorously and increases fire risk in the presence of fuel gases.
  • Must never be used for pressure testing or purging refrigeration systems because of extreme fire and explosion hazards.
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Key Safety Rule

Oxygen and acetylene cylinders must always be stored and transported separately, secured upright, and kept away from heat sources and ignition. Never use oxygen as a substitute for nitrogen or compressed air in any refrigeration system — the consequences can be catastrophic.

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