1995 Dodge Caravan

The system is run by vacuum. See if the small vacuum hose that enters the van by the heater hoses has come off, or it may have a check valve or resevoir that is leaking vacuum. When this occurs, you'll have air blowing from the defrost only. If that's the case, trace the vacuum source. It's usually near or at the front master cylinder. The power booster was used. It's under the hood. Ok