Air Conditioner problems of the 2005 Ford F-250

The contact owns a 2005 Ford F-250. The contact purchased the vehicle in January of 2005. Six months later, while driving approximately 45 mph, she heard a loud popping noise and the air conditioner stopped working properly. The air began coming from the defrost vents, but it was no longer cool air. The dealer and mechanic stated that the vacuum pump was defective. The vehicle was repaired, but the failure recurred and has persisted for the last three and a half years. On six occasions, the dealer and mechanic stated that the failure was due to the vacuum pump. A couple of years later, she noticed twice that the air conditioning would operate normally when the headlights were turned on and off. The manufacturer was notified and a complaint was filed. The current mileage was 101,388 and failure mileage was 20,000.