I have a 98 Bravada and I'm having a problem with the auto temp control. I just had my motor rebuilt and now the heater/ac unit will cycle hot and cold. You can hear a vent or something moving behind the dash, but not sure what it is. I have been over the vaccum lines 3 times and everything appears to be right. I had no problem before the motor was put back in. Any suggestions or idea will be helpful. :banghead:

Sounds like a blend door problem, check out the all info here...

http://www.automotiveforums.com/vbulletin/showthread.php?t=710593&highlight=blend+door