Yesterday I got in my 2010 Chevy Cobalt after it sat for over a month. It was hot out, but my AC would only blow warm air. So first I checked the fuse and relay and both were fine. Then I checked to make sure the AC clutch was engaged and it was, so I figured it must need to be re-charged. I bought a can of AC Pro and hooked it up to the low charge port, but it showed in the green which the can said it didn't need recharging. The AC lines do not feel cold. Does this mean my compressor may be shot? How can I diagnose a bad compressor or what can I check next? Thanks.