There are notes, tips, and knowledge that you accumulate over the years when you’re an HVAC tech. I just found the following on an old pen drive and thought I would share. I don’t know where it came from:

Copper Tubing:

  • K type copper is thick wall hard tubing
  • L type copper is medium thick wall hard tubing
  • M type copper is thin wall tubing used for drains and plumbing.

ACR (Air Conditioning and Refrigeration) tubing is charged with nitrogen and sealed. Same as L thickness, it comes in both hard drawn tubing and “soft” rolls of 50’ and 100’.

Soft tubing is annealed (heated and then allowed to cool) to make it flexible and easy to bend and flare. Note: hard tubing can be softened, or “work hardened” soft tubing can be re-softened, by annealing.

  • Refrigeration tubing is measured by it’s outside diameter or O.D.: ¼, ½, 5/8, ¾, 7/8, 1-1/8, 1-3/8, 1-5/8, etc.
  • Plumbing tubing is measured by it’s inside diameter or I.D. : 1/8, ¼, ½, ¾, 1, 1-1/4, 1-1/2, 1-3/4,etc.

Rule of Thumb: Refrigeration “nominal” tube sizing 1/8” larger than the same nominal size plumbing pipe.

Tubing cutters are the best way to cut refrigeration copper. Ream out tubing. Reseal unused pipe.

Tubing benders are needed to properly bend soft copper tubing. Never use kinked tubing.

Flare connections: Use a drop of oil on the flare spinner.

  • For ¼” pipe and smaller: the exposed pipe to be flared should be set above flaring block about the thickness of a dime.
  • For 3/8” and larger, it should be about the thickness of a nickel.
  • You should never have to “screw” the flare nut onto the flare. Remember, too big is just as bad as too small.

Soldering: using 95/5 (tin/antimony) at about 500 F. to flow by capillary action into the joint. It is primarily used in plumbing and air conditioning piping. Note: clean the joint, use flux to reduce oxidation, heat the tubing (not the solder), & support the work.

Flux only to within 1/8” of pipe end, twist pipe to spread flux, clean off joint when soldering completed.

Silver solder: 45% silver solder flows at about 1200 F. Follow the same rules as soft soldering, but use the proper flux. When the joint is hot enough the flux will turn from white to clear and the flame turns green. Silver solder is best used on “dissimilar metals”, such as joining copper to steel on compressors.

Silfos is a solid brazing rod that uses a combination of copper and phosphorous as the filler metal and flows at about 1500 F. It also comes in 6% or 15% silver content for added strength. It does not use flux and is mainly used by commercial refrigeration technicians. It is the strongest copper-to-copper joint possible.

Note: small pipes (1/4”) or capillary tubes can be plugged shut if you use too much solder.

Nitrogen introduced into the piping at only about 2 psig pressure will prevent oxidation build-up on the inside of the pipe during brazing or soldering.

Swaging reduces the number of joints. The depth of the swage is the same as the diameter of the pipe.

A/C & R applications use “NPT” or National Pipe Thread fittings which are tapered 1/16in diameter for every 1” of pipe.

by Ron Walker


Ron Walker
Ron Walker

After retiring from the U.S. Marines and achieving his B.S. degree, Ron Walker entered the HVAC field. He has been an HVAC technician, service manager, and business owner. Working as a service manager, he spent many years training HVAC technicians to be more technically competent and really understand their trade. His passion for teaching and helping others resulted in the creation of HVAC Training Solutions, LLC.