1997 Mercury Villager Front AC question

We have recently purchased a 1997 Mercury Villager, in very good condition. Week before last, 2 days after purchase, we drove from Florida to Maryland, and it ran great. Except… The front AC would start out blowing hard and cold, and then after around an hour, although the vents still feel cold, and we can hear the fan blowing, there’s very little air coming through the front vents. The rear AC, in the meanwhile, blows plenty of cold air.

If we stop for 30 minutes, when we get back in the car, the front AC blows cold again and again peters out in about an hour.

Any ideas?

My guess is that the front evaporator coil is freezing up. The humidity in the air condenses on the evaporator coil. Under certain conditions, the condensate will freeze on the coil blocking the air passage. When you stop, the ice melts and the system then blows out cold air as it should. It is possible that the refrigerant in the system is low.