Milgard window and window air conditioner

I am considering replacing all of my windows (50 + years old) with Milgard Vinyl frame types. One person told me I could not or should not keep my window a/c if I do since the a/c would be bad for the new window. This doesn't make sense to me and I would like to retain the unit. It's a 5000 btu for use in a 10 x 12 home office. Comments? Suggestions?
Harry
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Did they say why? Ask the Milgard people.
--
Joseph Meehan

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