Heater not working

I have a 1999 envoy. A couple of weeks ago the airconditioning unit stopped working. The envoy not only blows hot air. It doesnt matter what setting I put it on it only blows out hot air. At first I thought it was a fuse problem but that doesnt seem to be it. Any suggestions before I take it to the dealership and give my first born to fix it?

A dealership trip is often a good first move. Especially when it comes to a problem that doesnt look like it has an easy fix.