When i first fire up the truck, it blows the ac through the defrost vents. after about 45 seconds it will blow out the dash. if i set it to blow out the floor or the dash and floor, it will blow out the defrost. on the floor setting it will not return to normal after any length of time. can someone please help. it is getting rather anoying.

by the way, its an 05 350 with the 6.0.

thanks

 

Defrost is the default path for air flow, so whenever it will not blow out other orifices you have to suspect weak vacuum due to a leak. I imagine that yours is marginal, and that is why it takes a while for it to change.

The vacuum leak is most often down at the 4WD autolocking hubs, but there can be other reasons for weak vacuum as well.

 

exact. vacuum problem. mine was a faulty 4wd selector valve next to the vacuum pump

 

thanks for the input. i had suspected something similar but just wanted to hear some other opinions before i took her in. thanks again.