Why does my 1999 Ford Explorer's air conditioner shut off/switch to defrost when going uphill?

I have a 1999 Ford Explorer. When I drive it uphill, or put the engine under even moderate load, the air conditioner switches from blowing through the normal vents into the defrost. I have taken the car to a couple of different mechanics who have been unable to solve it.



Thanks for your help!Why does my 1999 Ford Explorer's air conditioner shut off/switch to defrost when going uphill?there's a vacuum hose off or pinched or it could be a vacuum leak Why does my 1999 Ford Explorer's air conditioner shut off/switch to defrost when going uphill?Your vehicle is loosing vacuum to the controls. Locate the vacuum resevoir in the engine compartment and see if it will hold vacuum. If it does then start checking the hoses back to the control. You will find a leak somewhere.

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