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I have an F250 2002 diesel 7.3 and noticed when I was on vacation this summer that when I needed to go into 4x4 with the Aircon on, after a few moments the vents would go to the "Defrost" position. But when I went back to 2x2, the AC reverted to the dashboard vents after about 30-40 seconds.
Is this normal or is there a vacuum loss somewhere? Where do I start looking?