title says it all...

I have hot air coming from those speaker vent thingies by the dash that points towards the side windows (the mirror area) and also the defroster by the windshield when the fan is on. the other vents blow just ambient air which is normal. Now I'm not sure what is wrong with the AC, but why can it only blow air at 4? it will not blow at anything else...

so any ideas? common problem?