Someone nicked one of the return lines in the undercarriage and after a few years that nick gave up and there is now a very significant leak there. I have access to a TIG welder who can work on aluminum as long as it's on his bench. Is welding up that spot realistic?

I am almost positive this is the only leak, as all the way up to the moment when I heard loud hissing and fog coming from under the car, the AS was freezing cold.

 

At this point, as you stated, you know with high certainty that's the leak, if you think you can weld something in place that will meet or exceed the pressure of the line normally, why not at least give it a shot. I'd be willing to be you're maybe the first person here that could do it. Just note that the lines gotta be kept very clean when you pull it off the car, and when you're welding, nothing can get into the line from your repair. That will be the death of the rest of the system.

 

You do realize a brand new one is like $25.00 ... right?

 

In all fairness, he's not even mentioned what car he's referring to. That said, I recall the hoses on my 07 were a paired set, and were quite expensive. Was under warrantee for me, so not to big a deal, but I want to guess they were like $120 or $150 for the pair.

 

Rather like $400-500. This is a whole unit including both low and high pressure lines for AC and forward and return lines for the heater core. I've been around for quite some time, so when I ask a question, in 99% cases it means that I have done by homework and asking it makes sense.

 

Then, by all means, give that welding thing a go ...