I have an 04 mustang gt the air conditioner blows hot air when i'm sitting at a stop light but when I get moving it blows ice cold does anyone know what could be the cause of this please help me out
Yes. Likely the low speed engine cooling fan isn't working (yes this is correct. The default speed for AC on is the low speed fan). That's why the AC doesn't work when the car is stationary (no air flow across the coil). As soon as the car begins to move there's natural air flow over the coil.
Suggest start by confirming that the low speed fan is moving air at idle. Then confirming that the cooling fan works on BOTH high and low speed. Trouble shoot from there after it's know that the cooling fan is working correctly on both speeds.