1992 S10 heater problem??

I have a 1992 S10 Blazer. It is 4wheel drive, four door Tahoe version. It has the 4.3 TBI with 354,000 miles on it.
The air seems to blow through the defrost all the time. Air does go through
the heater and vents but still comes through the defrost. I looked at the heater assembly down by the floor and it looks like there is a hole in the side where their used to be a screww or something. If I reach in and grab the little arm inside that moves back and forth and stick a nail through the hole and keep the arm from moving back, then I have full heat with very little defrost. I can move to air and it does change from heat to air.
Is there a bracket or something that has fallen off? My wife and kids drive it so they may have found something on the floorboard and tossed it.
I also have a vacumn leak on the controller but that as my fault not geting it back together and aligned properly. I will redo that after fixing the blower switch. It melts about once a year and I have to clean up the contacts and put the switch back on.
--
Lannie


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Sounds like a vacuum problem. I just did a complete tuneup on my Blazer today and noticed one of my vacuum lines was old and decrepid and had sucked itself shut. I redid the lines (one is a feeder line to the heater control) and now my heater functions work like they should. For a long time I could only get floor heat and hardly any defrost, I believe this made a big difference but wont know for sure till I need the defroster again....the heater directional functions (floor, defrost or front panel) are vacuum controlled.
On Apr 21, 8:16 am, "Lannie Schafroth" <lannie at ct-iowa dot com> wrote:

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Lannie Schafroth wrote:

The vacuum leak is likely the problem. The door that switches the vents from floor to defrost is vacuum controlled. The default position of the door is defrost. The leak means it stays on defrost.
--
Steve W.
Near Cooperstown, New York
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had a 90 Blazer once with a similar problem and it had a broken plastic clip in the bottom of the heater box that controlled the door operation. It was(at the time) a GM only part(and may still be)and hopefully it won't be discontinued at this point. It also was(WAS) about a buck or so. If you suspect this(at some point), hopefully you have a diagram of this system(or can get), take apart the lower part of this 'ductwork' and look up from the bottom and hopefully(or not) you'll see what I saw. Maybe it is what others have said it was and if you have a leak near the control head, I would fix this FIRST but after reading your issue-this(above) is what popped into my mind(****). There is my two cents worth and today it is on sale for FREE! Good luck-JP
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