On a R-22 system, must the discharge line pipe joints from the heat pump outdoor section that goes to the expansion device in the indoor unit be brazed or can it just be soft soldered? Since the temp of the discharge gas on a conventional heat pump is below 200 degrees and the pressure is below 300 pounds, I believe that the solder can withstand that temp and pressure. I plan to remove my split system air conditioner and replace with a heat pump and I would like to know this before I remove the piping.

Many older R-22 units were soft soldered at the factory so I think it would be OK for you to do it now. However if you ever wanted to use "Puron" (410-A) the lines would have to be changed because of the high pressure that the "Puron" operates under.

You can use a product called Stay Brite by Harris this material contains silver which is just what you want in this case. You can still use a hand torch but it is much better than 50-50 or 95-5 solder.

I braze all my joints with 15% silver stick and use oxyger and acetylene only. With this set up I can get on and off the joint quick because of the heat is fast. I always wrap all items that can be damaged with a cold wet rag or Zorba the heat or other products like it.

Warning. It is not how strong the alloy is so to speak. It is the vibration, along with pressure that makes a diference. I have seen many soft solder lines leak after a very short usage time.

Stay-Silv 15
For many years the standard of the industry, the 15% silver alloy has proven its value. This filler metal is excellent for situations in which close fit-up does not exist, and where agitation and vibration in service are involved.


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The Harris Products Group - Brazing, Soldering & Welding

For me personally I will tell you to NOT soft solder any refrigerant piping. Yes it has been done and also yes it has failed. Save yourself the trouble and do it right the first time. If you do not know how to braze then hire someone, for that fact unless you are certified by the EPA it is illegal for you to be messing around with refrigerant.