'98 Windstar - Low air flow from vents, etc.

I was on a long highway trip. Turned A/C on, and everything was fine at first. After a while, air flow through dash vents diminished, to the point where there was virtually no flow, though the fan was working. Tried switching to max. A/C, defrost, split floor/vent, split floor/defrost - no difference. Accelerating, slowing down - no difference. Rear A/C was fine throughout.

Near end of trip when I switched A/C off and turned dash vents on the air flow came back. It took a couple of minutes, but the air flow slowly returned to the expected level.

What's going on here - is the air blend door motor sticking or should I be looking for a vacuum leak somewhere? I'm quite concerned, as I will soon need to be using the defroster vents and floor heat, and there was virtually no air flow out of anything while this problem was occurring.

I have the same problem
anyone have any ideas

I’ll almost bet it’s you’re A/C’s condenser freezing up. When this happens, the condenser (which is basically a radiator that cools the air traveling through it) freezes into a solid block of ice. The warm, humid air coming from the outside of the vehicle travels through the condenser and cools. When it cools, the temperature drop forces the water out of the air and it condensates on the condenser coils. The water should then drain through a tube to the outside of the car. But the water on your condenser is freezing before it can drain, blocking off the airflow to the vehicles interior. When you turned off the A/C and just ran the vent, the ice melted and the airflow returned. Next time it happens, park the car and turn on the vent to full speed. I’ll bet you’ll see water poring out the bottom of the car within a few minuets as the ice melts.
What is causing it to freeze? The system could be under or over charged with freon. (It seems weird, but I have seen home A/C systems freeze from being UNDER charged). Or, it could have just been a really humid day and you had the A/C on max and the fan speed on low. If you keep the A/C on Max and the cabin is already cool, the cool air gets re-circulated back through the A/C system. This cool air combined with a low airflow, (because the fan is on low) could cause the condenser to become so cold that it freezes the water before it can drain. If you think this might be the case, you might try switching the controller to the normal position when the cabin temperature gets cool. This will blend in some warm air to help keep the ice melted.

Hope this helps,
TOM

I think Tomb Stone is on the mark.

The system is designed for both liquid refrigerant and gas refrigerant to exist together in the condensor (in front of radiator) and the evaporator (in the cabin plenum). In the evaporator (almost always installed upright), the compressed refrigerant is allowed to "boil" from a liguid to a gas ... this cools the evaporator.

As the refrigerant leaks away from the system, the liquid level drops lower and lower in the evaporator ... this means more of the volume in the evap core is filled by refrigerant in the gas phase ...more gas means the evap is colder ... the evaporator gets so cold it freezes water out of the air flowing thru the coil.

That is, up to the point that the system no longer works.

I would check the refrigerant charge before the system gets too low.

Also cleaning the core and the fan wheel will keep the air flow high.