a/c blows ice cold, then warm, then

My 00 envoy w/ auto air every once in awhile will blow ice cold then out of the blue blow warm air like a banshee, seems to last like 5-8 minutes then back to ice cold 72 degress like I set it, any ideas before I take it in?

My wife's Envoy did that. The dealer changed a pressure valve and that fixed the problem.

I know this post is older, but there is a TSB on this issue.

TSB#
03-01-39-007 MAY 03 A/C - Intermittently Inoperative/Blows Warm Air

If you have this problem and bring the vehicle in, sometimes you have to tell the dealer (not always, but I do) about the TSB. They dont always check the TSB's like they are supposed to and I once had my Chrysler Sebring (first mistake) in the dealer 5 times for a front end noise that if they would've checked the TSB's first, would've been fixed the 1st time I brought it in. Got a lot of free oil change coupons for that little goof up.