Every summer when I get a chance to turn on my ac on a hot day when my car been warmup already, while pressing on the break toward a red light or stop sign, the rpm drops quickly below 500rpm making the car feel like it's about to stall out and the needle goes back to normal idle. Only happen when ac is turn on and its a Honda.

When using the ac on a hot summer day,or a mild spring day,the compressor runs all the time.If you set it to low,and turn the temp to cold or toward the warmer side,lets say cool,then the ac compressor runs also,it just cycles,on,and off.No matter what setting you are using on your ac control,the ac compressor stays on,using fuel.Get the most out of your ac,while it uses your fuel,to keep you comfortable.All vehicles have a MAX setting,or a recirculate setting.Always use this setting.I say,always use this setting,not only that,but use this setting.I stress this because you are pulling in air ,from the out side,that is warming the evaporator,and making the ac work harder to give you comfort.In the hot ,hot summer,the settings MAX,and recirculate,keep the air that is in the vehicle,in the vehicle.It recirculates the air,instead of bringing hot air inside the vehicle ,and bringing the temp,up,to a warmer temp.A lot of people don`t even know that this is on the control,or don`t know what it is for.Some times the recirculate button,or dial,will have a picture that looks like a C,but squared off at the corners.So folks,get more out of your vehicles cooling and heat system.Yes ,this will work on heat also,maybe not defrost,but on some cars,it will work.