Heat / Air Problem

[jbragg]

When I am driving, the heat and air blows out great... BUT
when I am just sitting still, like at a red light, it blows cold air (when I want heat) and heat (when I need cold air).

What is the problem here?

I am not great with cars, so I will need some serious help.

Thanks in advance

[jbragg]

anyone?

[jbragg]

plus...
my car almost overheats.

When I am at a stop... and air is on, it does not blow out cold air and my car rises from being in the middle of low and high to high (almost to the red mark).

When I accelerate, the air comes out cold and the gauge goes back down (instead of overheating).

Someone help me out here... is it a bad thermostat? The coolant level is filled and the cooling fan is working.

PLEASE HELP ME OUT