2002 1500 SLT quad cab 5.9L. My air conditioner puts out hot air when I am driving around town. When I am on the hiway it works great. What's the problem?

 

One quick thing to check - Start the engine, turn on the AC, turn the blower to medium, temperature dial to cold, and open the hood. Make sure the compressor is turning and make sure that the condenser fan is blowing (not the main radiator fan, but the one off to the side).

If all this is working and assuming that the condenser isn't clogged up with bugs and dirt, it could be a low refrigerant charge. Perhaps one of the folks more familiar with the AC system can chime in here.

 

Like Tom suggested above. If the compressor is turning and its still not blowing cool then i'd say low refrigerant.

 

The same thing was happening to mine. The condenser fan and compressor were working fine, I shot some more refrigerant into the system and it's freezing my wife out now. Not a bad deal for a couple bucks!

 

Most guys find that when it is not cold at idle but cold during driving then the condenser fan is not working.