soldering aluminum to copper

[loman]

I'm thinking about changing out my aluminum barbed fittings on my tranny cooler to -6AN fittings. The original fittings are aluminum and soldered to the copper cooling coils. I was always told you can't solder aluminum to copper. Has any one had any experience in soldering aluminum to copper?

[vicegrip]

It's doable but only under perfect conditions.First,the AN fittings are probably anodized and you must get all of that off before starting,either by blasting or with sodium hydroxide which would be lye,regular fuming oven cleaner,or drain cleaner which is close to 100% sodium hydroxide.Get the Muggy Weld Super Alloy 1 starter kit (expensive) and give it a go.There's all kinds of solder kits that claim to work and their reps make it look easy but their conditions are perfect and in reality,my personal success percentage is low. You might get lucky but I'm guessing you probably will end up ruining the cooler and getting a different one.
How much copper tubing is sticking out after you remove the barb fitting? Is it possible to use a flare to AN fitting? Or use a compression to AN fitting?

[StPro]

Another option is to silver solver a steel hydraulic fitting with sta-sil 15
http://www.harrisproductsgroup.com/en/P ... lv-15.aspx
You could even sta-sil 15a male or female copper adapter on the tubing and screw a an fitting on.

[Rocket989]

My brother's a union pipe fitter and instructor ...just asked him, he said "Nope". x2 on flare to AN adapter!!

[ElGuapo]

It *can* be done, but you just about have to do it in a nitrogen atmosphere and have everything else absolutely perfect.

You can get brass -6 JIC fittings through various outlets that will readily accept aluminum AN threads.

[loman]

A friend of mine works in the HVAC field and he said some of the new a/c coils are made with aluminum and it is soldered to the copper line set going to the condensing unit. He even sent me a picture the other day of the soldered joint. He said the manufacturer solders a piece of copper on the end of the aluminum line. That way when the unit is installed in the field all the hvac guy has to do is solder copper to copper. So I'm guessing with that the manufacturer has a controlled perfect environment when doing this. I asked my buddy what would he do if that aluminum to copper joint started to leak. Resolder it or replace the whole coil and he said replace it.

I probably should have mentioned this in the original post. I have a different friend who is a racer. He actually gave me the idea of soldering a fitting into my cooler. He done it 10 years or so on his car. He unsweated the barbed fitting. He then took an aluminum fitting, stuck in a lathe and milled it down to where it barely fit inside the copper line. He soldered it (he thinks he used silver solder) and has never had a leak. He has been racing the car ever since. His theory is just because someone says you can't do it the correct way, doesn't mean it can't be done and made to work. If it isn't leaking, it must be ok.

[loman]

Here is my cooler now. I bought it from Summit. As you can see it has an aluminum to copper connection from the factory. I don't believe there is enough room for a compression fitting. I think what I might try is to cut the barbed end off flush with the aluminum body. I believe there is enought meat there that i can drill it out and put some threads in it. Then all I have to do is buy the correct fitting.

[Rocket989]

Yeah, the bro said same as above regarding new production stuff but pretty hard to do properly in the field though you can get lucky. I guess there are epoxies intended for this if needed. Silver-bearing solder likely but I think you'd need oxyacetylene to braze with actual silver solder rods.

Looking @ the cooler, I'd measure the OD of the fat part and the area behind where it necks down & see if any off the shelf fittings will fit. If you got a copper sweat to <whatever> pipe thread, you'd be set...just need the correct AN adapter(s). Shucks, then you could even use brass unions/ adapters and save the $$ of the AN stuff...JMO...!!!

[loman]

Well, I guess I was worried about nothing. I cut off the barbed end and drilled and tapped to 1/8" NPT threads. I still need to flush the cooler real good to ensure all the aluminum shavings are gone. I'll buy a 1/8" NPT to -6 AN fitting and proceed making my braided steel cooling lines.

[Rocket989]

Sweet, like it when stuff is easy!!