'94 F150 fan issues

[Ryan_V]

My old ford is giving me a little trouble. Every once in a while, with the heat or A/C on, air stops coming from the vents. The fan is still blowing, I can hear that, but air flow stops. then after a while, it will pick up again..... any ideas???

[Jeremy airjer W]

frozen evap core. If it happens in defrost or a/c than that would be my first thought. If it happens on the other heat settings with the a/c off than Hmmmmmmm?

[Ryan_V]

frozen evap core. If it happens in defrost or a/c than that would be my first thought. If it happens on the other heat settings with the a/c off than Hmmmmmmm?

i think it happens with everything. the last time it happened was last week when I was just running the vents with no a/c.

[Jeremy airjer W]

Is it moving to a different position. For example you have it set on vent your driving along and it changes by itself and starts blowing out of the defrost or floor. If that's the case than there is an issue with vacuum supply (pretty sure these are vacuum controlled, somebody correct me if I am wrong). Typically when there is no vacuum manufacturers will default the air flow to the defrost position to keep the windshield clear.

[Scott K]

Spot on airier!

[Ryan_V]

just seems to disappear. comes out nowhere. next time i'm in the truck I'll see if I can get it to happen and pay close attention to what happens!!