I have a 2000 Tahoe, near same problem. Control stuck on dash vents (cannot select defrost or floor heater from dash climate control. Rear heater seems to work okay, haven't confirmed any problems for rear control) Overhead temp sensor sounds like a speaker most times (buzzing). Main problem is vent on passenger side seems to be locked open (cold air at high speeds only on passenger floor vent area, heat from dash vents works and driver floor doesn't have cold vent air). First, I would like to fix the control to have defrost (very important immediately), dash, or floor air control (I can select temp on max heat or max cold as I think the climate settings are unreliable due to temp sensors could be bad and if I want heat, I'll select heat. If I want cold, I'll select cold, eh?). I almost ordered a $80 control module, but don't want to waste money. Also, how can I close the vent beneath the dash on the passenger side for now so my wife doesn't get frozen feet?

 

I have a 2001 Tahoe with the rear a/s control switch does not turn on the fan either hea t or air...could it be the conector (I think 7 pin)