Fan quits on acceleration

[ericj14]

I have a 99 Safari AWD, 113,000. This started last week, during dog days of summer. When I turn in the interior fan whether its AC or not, it works fine. Then when I accelerate and even sometimes maintain current speed, the airflow stops. I can still hear the fan blowing, but there is nothing coming out of the vents. When I slow down, or go down a hill where the engine doesn't have to work, it kicks back on and works fine until I accelerate again. Anybody else have a problem like this? I can't think of what it could be.

[Blue Bowtie]

The next time you experience the problem, reach above the dash pad and feel for air exiting the defrost outlet. I'm guessing that all your air is being dumped there.

[old_master]

One of two things: either you have a small vacuum leak in the HVAC system reservoir, lines or control, or the check valve located under the hood near the evaporator housing is defective. Insufficient vacuum will cause the system to default to the defrost position as Blue Bowtie is suggesting.

[ericj14]

Thanks a bunch for the replies. I'll take a look next time I drive it.