House Air Conditioner is leaking freon.

I'm having an issue with one of the Air Conditioning systems in my house.. For some reasons only the upstairs unit seems to be leaking freeon. He tried using the bubble detector solution, but wasn't able to find any leaks with that. He did this in both places, in the attic near the coil, and outside by opening the unit near the compressor..

He said that the only other place that the freon could be leaking is in the pipes from the upstairs unit to outside, which would involve drilling a hole in the wall, pulling the pipe out, and replacing, and then repairing the whole in the wall.

However, when the tech replaces the freon (with up to 2 pounds of freon), the Air Conditioner is ice cold again, and the last time he recharged it, it lasted for 2 weeks. Hopefully this time it will last longer, and the summer in the SouthEast will be over.

I've also replaced the filters and vacuumed the vents.

Have you seen this before.. where the freeon leaks over a period of say 2 weeks, but can't be detected, and upon recharging, it works fine.. for another 2 weeks. ?

Thanks in advance for your help..

That's a pretty well written description. IFF the tech was reliable and you have a leak in the walls, it seems funny he wasn't able to detect it anywhere. If it's leaking into the walls, there has to be an exit point for it and it'll be detectable there.

If it's actually "freon" as you said, that has a pretty good odor and at the loss rate you indicate, you should be able to smell it yourself, even.

Did the air conditioning tech use a refrigerant leak detector? This tool can "sniff" out a freon leak and tell you where it is located.

Also, if this is in the attic, I don't know why a hole would have to be made in a wall. It should be pretty easy to pull out the old and fish in a new pipe. Just my two cents; I know it isn't my money, but if I were you I think I'd try another service and if they came up with the same results, consider replacing what needs to be done. It's still cheaper than paying housecalls for freon every two weeks in your climate.