AC intermittent

I have a 2000 Nissan Xterra, 87000 miles, V-6 3.3, auto. And 2 wheel drive that I purchased new and has never had a single problem. The AC works sometimes from the 1st start of the day blowing cold air, other times not at all and still other times after repeated pushing of the on/off switch for 30-60 minutes. I've taken it in and no leaks were detected and freon is full. One tech said it was probably the AC computer control module needing re-programming another said they've worked on many Xterra's and never had to re-program a module, any ideas?