Hello I'am driving a 92 aerostar 4.0 when air conditioner is blowing from vents as I accelerate or go up hill blower switches to defrost then returns to vents when it evens out. Is there a simple explanation for this? thanks..
When you accelerate the manifold vacuum drops. There are vacuum operated "motors" under the dash that operate the doors that direct the flow of warm or cold air in the cabin. One of your vacuum motors may have a leak in the vacuum chamber (diaphram) and the drop in manifold vacuum is not allowing the "motor" to hold its position. It is another possibility that you have a vacuum leak elsewere in the system.