I actually have a 1998 GMC Jimmy so please don't shun me. My climate control has started cycling back and forth from hot to cold coming out of the face vents. This happens when it is on all auto. I can't seem to control it manually either. The only thing I've been able to find online is that perhaps the control motor on top of the heater box has gone bad and does what it wants to. Anyone with this experience?

 

I'm not sure, but maybe. I have 99 Blazer with climate control. It I set it to 74 degrees it will blow hot and then cool. If I put it all the way hot, 82 I think, it will stay hot. I just put it all the way on hot when I need it warm, otherwise I don't mind the back and forth, too much.