2003 Ford Windstar A/C vacuum

Hi Don Polston. Welcome to the forum. This is typical of vacuum-controlled HVAC controls. Look for a check valve in the vacuum hose going from the intake manifold to the firewall. If it is not defective, ask the dealer about an updated valve with a small storage canister built in. The normal loss of engine vacuum is causing the change in where the air blows from. The systems are designed to default to the defrost position when there's a problem with the vacuum source or controls. It's a safety thing. Your feet might freeze in winter, but you'll be able to see. If an improved check valve isn't available from Ford, get one from a Chrysler dealership. They had the same problem and the larger valve solves it very nicely.

Caradiodoc