I have a 98 f-150,i do not understand this problem,after driving for about one hour the a/c stopps blowing through the vents,the blower fan is still just blowing away loud as can be but not through the vents or def or floor nothing, i went to ford and talked to the pts guy and he told me to replace the ac/heat/def switch he said this is a common problem replaced it that same day went for a drive same thing.any help would be great,thnks Mike.

 

If you're absolutely certain that no air is being moved anywhere in the system, then there is only one likely explanation.

The squirrel cage portion of the blower is loose from the motor shaft.

Steve

 

The cage is still on because you can hear air going in the dash some where,what i have to do is turn the selector switch to another position for just a few minuits then turn it back to max a/c and it works ok for 30 more min or so?any ideas would be great thanks Mike.....

 

Could it be freezing up????


You say it only does it when its on Max. And if you turn it to another position it clears up?

After 30 minutes on Max it seems to come back???

 

An iced evaporator is a possibility. It does have several symptoms which have not been mentioned:

A clammy feel to the airflow just before flow is blocked and sometimes after airflow is restored.

and

If the vehicle is parked while there is no airflow, a VERY large puddle of water will form under the vehicle over the next half hour or so.

Evap iing is usually due to an undercharge.

Steve

 

Could also be that your blend door is sticking or broken.

 

No. The blend door cannot stop airflow. It can only redirect it inside the plenum.

Steve