a/c, heater control problem

I own a 95 blazer and when the air is blowing it is always coming out the bottom vents. No matter what setting I have it on. When I'm using bilevel a/c it works great when I am just cruising at a set speed, but when I need to give it some gas it seems the fans kick over to defrost and stop coming out of the dash vents. When I'm trying to defrost my window in the winter the bottom vents are blowing all the time, even though I have it on defrost. Is this a common problem or is my heat controls just screwed.

Any help would be apreciated.
Thank you

I own a 95 blazer and when the air is blowing it is always coming out the bottom vents. No matter what setting I have it on. When I'm using bilevel a/c it works great when I am just cruising at a set speed, but when I need to give it some gas it seems the fans kick over to defrost and stop coming out of the dash vents. When I'm trying to defrost my window in the winter the bottom vents are blowing all the time, even though I have it on defrost. Is this a common problem or is my heat controls just screwed.

Any help would be apreciated.
Thank you

Check your vacuum lines going to and from the intake and to the HVAC controls.

I had the same problem all it was is the vacuum line got disconnected from my vacuum conister under my hood.

thanks ill try that, much appreciated

I had the same problem all it was is the vacuum line got disconnected from my vacuum conister under my hood.

Good call, it is the vacuum ball in the drivers back corner of the engine bay, it will often come loose or the line will rot and will need to be replaced.

Winshield washer tubing is perfect for it.