why doesn't my defrost or radio controls work in my 1992 chevy silverado?

[michael]

i'm not sure why but my defrost doesn't work and my radio/heat controls won't work. When you press one of the buttons it acts like its going to work, but no changes occur, can anyone help me out?
the lights and displays all work on the radio and climate control but it does not respond to the buttons when pushed. It cant be the fuse because its getting power. I was thinking maybe a relay??