Blower fan query

[Mwlock]

Why would my blower fan reduce speed or stop when I am increasing speed on the highway and then kick back up again?

 

[Uncle Gump]

Your vacuum reservoir under the hood is broken.

 

[RonD]

+1 ^^^^

The Cab vent doors, i.e. defrost, panel and floor, are vacuum operated, defrost is the default air direction, low or no vacuum

Vacuum is supplied by running engine, same as power brake vacuum
There is a Vacuum reservoir in the engine bay, so the Cab vacuum system never runs low on vacuum when engine vacuum is low, like when accelerating

Its a black plastic ball located down low on passenger side front of engine bay, look from under front bumper

If reservoir can't "hold" vacuum then vent positions would change to Defrost vent when accelerating, check if that is happening
If so then thats the issue, loss of vacuum in reservoir


Very unlikely for it to be an electrical issue, or you would have also mentioned dimming lights when accelerating, so alternator fault