I also have a similar issue. The Coolant is full, we've replaced the switch and I am still having these issues.

Most of the time, it works but living in the humid summers, I need this working 100%.

Leaving the back window open seems to have an effect of lasting much longer and when the AC stops blowing cold air and essentially working as if on Vent, I switch to vent for a few minutes and switch back and the AC works for another extended period of time, sometimes.

Don't have the money to get someone to look it over and it is driving me crazy.

Please help. (also dunno why sig won't show up: 2002 mazda b3000 v6)