I have been trying to find the problem on my blazer for a week now, I have read every posy I can find on the topic but none of them are the same as mine.

I can not get the floor vents to work, I have checked the vacuum line that is by the pcv into the cab of the truck and it is fine, the vents will actuate from defros to the face vents but will not go to the floor vents, please help as I do not have the money right now to pay $90 per hour to take it to the dealer.
is there supposed to be a huge difference from the fan being on three than four, because about a second or two after I turn it to four it just starts blowing twice as hard as three?
Thanks in advance

 

I had this same problem. When you turn it to the floor, the heat continues to blow out the vent and/or defrosters, correct? (I think it was just defroster, but I don't recall). There is a diverter flap inside the ducts, and the plastic pin on it has snapped. To verify, lay down on the drivers side floor and look up under the dash (near the center, somewhat close to where the floor heat would come out). When you switch it between floor and defrosters, you should see a little part turning, but you'll notice its not quite attached right (sorry about the vague explanation...I don't remember exactly what it looks like). If I remember correctly, I was able to turn it by hand and get the floor vents to open up (though it wouldn't stay this way once I let go, so it's wasn't possible to just rig it to stay open partway).

It's a $5 part, but it requiresyou to take apart the entire dashboard. I started trying to do it myself, but when I realized how much was required to get at it, I was uncomfortable doing it myself. I paid the dealership to fix it. They billed me something like $450 for labor (2 years ago).

 

So I have the same problem. No heat to floor, it just blows out the defrost. I went under the dash and poked around and saw two actuators. A lower one and upper almost abive it with the white plastic arms and linkage. They aren't cracked nor broken.I am assuming the lower one is for the floor heat. I noticed the linkagesnaps real hard when going into defrost but it doesn't move when going to the floor vents. The upper one moves smoothly without the snapping noise. I do have vaccum going to the lower actuator from the red and blue lines. I was reading on this forum that it could be something inside the flap in theheating ducts but I can't see inside there. Maybe special mirrors would help. Does anyone have any good advice at how I can determine where the problem is? I am thinking the actuator. Any help would be great.

Thanks!

1998 Blazer 4x4 4.3L 155,000