Why doesnt my ford escape aircon provide continuous cold air when at highway speeds?

[IslandTech]

Today on out of town trip, several times the aircon just stopped giving cold air. Speeds were up to 110 km/hr. I turn it off for a few mins, and when i turn it on again it works. Then warm air again. Within the city when speed is only up to 60km/hr max, it hasnt showed this problem. When we got within city limits and driving slowly, aircon turned back to normal.

 

[sometimeswrong]

Vaccum leak in the dash controls or lines.