the ac goes on and comes out the propper vents but when you step on the gas and or reach a certain speed usually above 55 mi/hr but could be less the vents shut off except for some coming out the defroster. sometimes now it won`t even work at low speeds. the compressor is working as it should. it`s just that the propper doors do not seem to be opening. help

paul f., July 2006

As you acelerate you loose vacum ......and it will goto defrost mode .......you have a vacum leak to the ac control head
Look under hood and follow vacum hoses going into the fire wall ........might also be the 9 port vavle in the ac control head ...all are simple repairs

bg, July 2006