Model: Grand Prix
Make: Pontiac
Year: 2002
engine/transmission option: Automatic
are you mechanically inclined/have the right tools?: Don't know much about cars, might have the right tools
Issue(s): Air conditioning is warm air, heat is cold air.

Last winter, the heat in my car would go cold, and I would be able to fix it by moving the temperature gauge up and down a few times. But after a while, that stopped working, and I just had to deal with not being able to use my heat, because it was always cold. Now, it's summer, and my air conditioning only blows warm air.

This used to be my brothers car, and he thinks that it may be something to do with the thing that changes the source of air (inside/outside), and that it may have been messed up from something that a mechanic fixed a while ago.

Sorry for the vague explanation, but feel free to ask anything else, and I'll do my best to answer it.

Thanks

Checked your heater core, thermostat (if your running it open could be why its blows cold), on the a/c take it to a local shop normally they can tell you if your compressor is out or not, but an easier way to test is by ear. When you turn the ac on can you hear the compressor kick on? Check the a/c lines to make sure they have not been chopped up or burnt open, happened to an old car I use to have was a 150$ fix to replace the main a/c line and fill it with r34 again. Check those all I can think of at the current moment, I'm no mechanic by no means but I been in your situation.