overheating while idling in traffic and driving slow

fogot to add that i just had new a/c condenser and drier filter put in and started using the a/c again. now it is overheating sometimes in traffic and going slow. before this no problem with overheating. water pump is new but not thermostat. if fan runs on med does prevents overheating. my mechanic said he checked fans running. coolant is fine. radiator looks good. ????

I have personally experienced the following reasons for overheating while idling 1. Your fans may not be running and means during movement your engine is cooled by air as your car moves. 2. The coolent tempreture sensor that is supposed to fire the fans could be out of order. 3. Lastly your water path could be dirty.

You may also have your thermostat checked just in case its not opening in time