2004 Kia Spectra Dealership can't duplicate problem

Air Conditioning problem
2004 Kia Spectra Automatic 59,200 miles

I have a 2004 Kia Spectra. On hot days, the air conditioner will shut off after about 30 minutes on max air, but this is an intermittent problem. When the air conditioner stops, I can feel cool air around the vents, but it doesn't blow out. Taken it to the dealership multiples times (because it's covered by their 60 month/60,000 warranty). They can't "duplicate" the problem while they have it. Now I feel like they are wanting me to drive it out of the warranty without fixing it. Talked to a friend mechanic and he says it sound like a faulty high pressure switch that cuts the car off when it is over-heating. Does this sound correct? Any ideas on tricks to get my car to "duplicate" the problem while at the dealership? Thanks.