PONTIAC SUNFIRE AIR CONDITIONER BLOWS HOT

My 2001 Pontiac Sunfire Runs Good. Ac Pressure Is In Green. My Ac Blows Hot Air When Idling But Runs Normal At Highway Speeds.

My Air Conditioner Works Really Good As Long As I Am Driving 40+mph, The Minute I Stop Or Slow Down To Much The Temperature Gauge Starts...