The most common problem that causes vent operation problems is vacuum supply or loss. The fresh air vacuum diaphram has a high failure rate & can cause this any time the A/C compressor is on & you ask for A/C. Try pushing the EC button & then see if the vent problems go away.
ALSO under the hood there is a vacuum supply manifold(plastic) with 10 vacuum ports that CRACK & leak vacuum as well. There is also a vacuum storage tank under the rt fender that connects to that manifold as well. They also will crack as they are plastic as well.
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