I had the same problem last summer. I was cruising at freeway speed and the A/C would not go on it just blew out hot air. It only happened one other time other than that. A little weird. The thing I really cant stand is how it surges so bad especially in lower gears where it will actually accelerate on its own when it cycles on and off.

1998 SVT #95: Toreador Red - SHM headers,K&N Filter, Energy Suspension MM inserts, Cross Drilled Rotors,Redline Tranny Fluid, Custom Billet Aluminum Shift Knob