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Introduction to Brazing for HVAC Repair Technicians

Introduction to Brazing for HVAC Repair Technicians

Posted by Matt Krak

August 24, 2021

A lady pro using a blowtorch.

One of the biggest selling points for students entering the HVAC industry is that what you’re learning is hands-on and practical. Plenty of schools will advertise that their courses are meant for those who want to get their hands dirty out in the field. Most students enter the trades to learn valuable material that actually has a use case in the real world, and isn’t just theoretical or straight out of a textbook. Learning how to get the job done well is crucial for any trade student hoping to get out in the world and start making a difference fast. For HVAC techs, one tool you'll need to get familiar with is how to braze your system's joints well. For those of you who want to learn more, let's get right into how to service this skill.

How to braze tubing the right way

Having the proper amount of refrigerant in the system is crucial to efficiency and effective system operation. That’s why plenty of techs get started working by dialing things in on their AC units. One important thing to note, however, is that if you don’t check for leaks beforehand all of that work may go to waste. Now, every system leaks to some degree. Whether it's the hose you connect to the system or the fittings themselves, even the best installs will have some amount of leaking. That being said, it's important to know that mechanical fittings tend to leak more than brazed fittings. Hence, brazing can be an incredibly useful tool for reducing leaks and increasing the longevity of your system.

For those who don’t already know, brazing is a metal-joining process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, with the filler metal having a lower melting point than the adjoining metal. This process helps turn connections in your system into one stable piece, reducing the likelihood that coolant will leak out of any joints.

When attempting to braze try to avoid the following mistakes:

  • Brazing without nitrogen will corrode the copper tubing at high temperatures exposed to oxygen, which will flow into your filters.

  •  Sweating off joints (heating parts up to pull them apart) is a deadly service practice. Whenever you have to take systems apart, it's better to cut as opposed to heating and prying, first because of the safety element. Sweating off joints tends to have them pop apart, which can lead to oil being exposed and catching fire, which all around will ruin a lot more than your rating on Google. Another reason is that you’re more likely to release more moisture into your system, which will damage your filters.

  • Sanding copper after it's been cut is a rough practice because it can introduce tiny shards of copper into the system. Clean the copper first before cutting and you’ll have a much lower risk of damaging your system.

When you decide to braze, the goal should be to get the base material of the joint between 1200 - 1300 degrees. Visually, that is between medium cherry and dark cherry; the temperature color change you want to see on that copper joint before you begin to apply the rod. The easiest way to reach this level is to get your torch up to it, and if it starts to get a lighter color than dark cherry then back your torch up.

The reason we want the joint at this temperature range is because the silver rod will typically only melt well at this heat level. Most rods are typically 15% silver, so you’ll need a high temperature for all the different metals to melt and create that seem in the joint that’s required for a proper bond. 

Another important tip for a proper braze is that your torch has either a carburizing or neutral flame. (See the diagram below).

The reason your flame type matters is that an oxidizing flame (as the name suggests) oxidizes the joint which makes it weaker.

Here are a few of the best practices for brazing:

  • Brazing with nitrogen flowing at 3 - 5 Standard Cubic Feet / Hour (SCFH). Flowing at this rate helps displace oxygen and water vapor that would otherwise be leaking into your joint and system. 

  • Wear proper safety equipment and PPE. You’re going to need at the very least proper eye covering and a mask to protect yourself. Some sources even say to wear darkened or tinted safety glasses to protect your eyes from the minor radiation that comes off your flame. 

  • Cutting off joints (as opposed to heating and prying)

  • Sanding copper before its been cut

  • Deburring only when it's safe to do so (meaning you won’t drop anything on the system’s lines)

  • Allow the copper to melt the alloy in your rod, not the flame

  • Protect your work area and your components (have a fire retardant cloth or towel to help prevent fires) 

Using these tips, you’ll be brazing like a pro in no time. 

These tips were adapted from a stream provided by our friends at the HVAC-R School. For more information and safety tips, feel free to check out the original video here.