How long of a vacuum until braze safely with r290

[Bobinater33]

Every time I release all the r290 to fix a leak I pull a vacuum for 30 minutes or so and hope it’s safe to apply the torch to. Every time though it feels as though I’m just getting lucky that it doesn’t explode in my face.

I’m sure a measurable quantity of propane remains as bubbles in compressor oil as well as in pockets throughout a coil regardless of deep vacuum. I can also see green and red speckles coming from the pinhole leaks that I can’t tell if it’s from running solder metal flakes or if it’s propane. I’m almost certain it is propane vapor.


Reminds me of that video on YouTube where they apply a direct flame to a large tank of propane. It took some time (so does brazing but brazing applies a much hotter more concentrated heat) but it eventually exploded violently even with a pressure relief valve.

[u3b3rg33k]

to be safe you need to not have air (oxygen) in the system. you don't need to pull a vacuum at all to braze, just purge with nitrogen. You don't want to be heating propane gas (or compressor oil) to red heat in a pipe anyways, oxygen free or otherwise.

a 100% propane atmosphere isn't flammable.

Propane Limits of Flammability - The lower and upper limits of flammability are the percentages of propane that must be present in an propane/air mixture. This means that between 2.15 and 9.6% of the total propane/air mixture must be propane in order for it to be combustible. If the mixture is 2% propane and 98% air, there will not be combustion. If the mixture 10% propane and 90% air, combustion will not occur. Any percentage of propane in a propane/air mixture between 2.15% and 9.6% will be sufficient for propane to burn.

https://www.propane101.com/aboutpropane.htm

also unless you're holding a torch to your entire system at once, you're unlikely to "blow up" the system. brazing a joint is not the same as holding a torch to a receiver/grill tank.

[Bobinater33]

Awesome thanks for the clarity!