I have a 2002 Lexus LS430, When I go to the Climate Section all the buttons are greyed out and not responsive. I've tried 3 differient Nav screens and I have the same issue with every one. I have double and triple checked to make all the connections behind the screen were connected. The lights on the physical buttons don't work either.

 

I had the same problem. I changed out the AC amplifier and problem solved. The AC amplifier is located behind the glove compartment, so the glove boxes unit must be dropped down. An AC amplifier on eBay cost me $45.