My a/c and heater will only blow through the defrost vents. Why?

 

bad vac line, check the white line under the hood, by the heater box.

 

Ditto, I had the same problem a few years back, can't remember if the hose was loose/cracked.

 

most of the time they are very very brittle, and cracked,

if you replace it find a hose about the same diameter, if it is to big it wont have enough vac to work.

 

When this happens you have lost vacumn to the control swith (floor-vent-defrost-ect)this is a default build into the system at when it fails it wiil default to keep windshield clear.you just have to trace to lines and look for a leak.The most common problem was the vacumn can would rust out.

 

Thanks guys