I am having a similar problem... the temp down button on the drivers side occasionally works. BUT here's the odd thing... when it does work (when is successfully drops the temperature by one degree) it also switches on the radio and flips it between AM and FM. Even if the Radio is off... when I hit the temp down button, the radio will turn itself on and go to AM. If I get it to work again (after several attempts) it will switch to FM.
This is a 2011 CTS-4 with no navigation.
This is a 2011 CTS-4 with no navigation.