Chrysler Repair: 2000 300m overheating, cross flow, traffic jam

Question
My 300m overheats in stop and go traffic with the a/c on. I just fixed the a/c compressor and have not had a problem with the car unless the a/c is on. Today I hit traffic jam and it instantly started to heat up to red. shut off and cooled down and started again when traffic was moving, no problems. opened the hood and 0verflow tank was boiling and the fans were on. Replace the water pump and timing belt 2 years ago. With out the a/c on never had a problem with traffic.

Answer
Hi Scott,
I wonder if the radiator may be partially clogged. Touch the left and right side manifolds of the radiator to see if they are of similar temperature. If one is much cooler than the other then that would suggest you need to flush the radiator to improve the cross flow. Also are you using a 50/50 mixture of coolant?
Roland