A/C on 2007 Cobalt blows warm at idle possible fixes
Time to have it serviced. It's probably low on refrigerant. That could be because of a leak so its best to have the pros take a look. Could also be an issue with the blend door in the ductwork that changes it from heat to cool depending on your settings.
Search Chevrolet Cobalt Questions
Chevrolet Cobalt Experts