have an 07 gmc acadia with 50,000 miles…on trips of 45 minutes or more the ac starts blowing just vent air and barely enough to move a tissue if held in front of it… sometimes it sounds like it is blowing really hard under the dash but not coming out of the vents. Sometimes you can cut it off and crank it again and it will be fine but most of the time it takes atleast 30 minutes of just cutting it off to get it fixed…
At times ice can form on the evaporator coils and block airflow if a switch called a low presure cutoff switch does not work correctly. They are usualy under 20.00 and can be replaced without loosing your refridgerant charge (they screw in a fitting on the accumulator, the accumulator is that large aluminum can with large AC lines going to it)replacing this would be a reasonable action when no AC diagnostics is possible.
thanks for the advice…I will print your suggestion and have a mechanic give it a try…Thanks so much…