why does ac only blow from bottom vent?

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staxxs

Not-quite-so-new-guy
Sep 29, 2012
36
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6
my ac use to blow from top vents now it only blows from the bottom. is this something I can fix or do I need to take it to the pro's? thanks
 

staxxs

Not-quite-so-new-guy
Sep 29, 2012
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6
Pico79 said:
had the same issue on my 79, I replaced some of the plastic vac lines in the engine compartment and that solved the issue
thanks ill try in the morning
 

rickyric

Not-quite-so-new-guy
May 30, 2013
10
0
1
Getting ready to do the same thing.Replacing the selector switch first then the lines if need be. The car set up in a basement for 16 years, just recently had the ac system converted to 134. It's cold and blows great, but max, normal and bi-level all blow from the top vents and the bottom vents. I'm trying to get the bottom to close.
 

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83hurstguy

Not-quite-so-new-guy
Jul 28, 2010
39
0
6
Kansas City
The floor vent defaults to the open position and uses vacuum to close when you have "Vent" or "A/C" selected. The vacuum comes in from the engine compartment, goes through the back of the A/C switch panel (there's a vacuum switch that changes position with the sliding levers), then distributes underneath the dashboard. I fought issues with 2 bad vacuum switches on mine (yes, one out of the box was bad brand new).

A chassis service manual will help you diagnose this. You can use a handheld vacuum pump to actuate portions of the system, or you can pull apart the connector behind the glove box door and manually jumper vacuum signal around to various components. The vacuum signal goes in through there, heads to the control head, then distributes back out through a connector there. If you know what the color codes are for, it's easy to jumper.

My bet is you either lost the vacuum signal (hose came loose from the accumulator ball or at another connection), or the switch on the back of the AC control head is bad. The worst case option is that the actuator for the floor vent took a dump, that can't be fun to change. Once I knew I had a vacuum source under the dash, I used a vacuum pump on that actuator under the dash, and when it moved, I knew I obviously had a controller issue somewhere.
 
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