Under dash air box hvac.

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duece1951

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Fort Myers, FL
First Name
thomas
Truck Year
1984
Truck Model
GMC C1500
Engine Size
305
Hi everyone! New here. I bought a project truck, 1984 GMC short bed with air conditioning. Sat in a barn for 10 plus years. Runs and drives. I have vacuum to the system but the vacuum does not close the dash vent door completely. Last night I noticed an air leak sound seemingly from behind the box under the dash. Question is, can I remove the rear vacuum control and check for leaks or am I in need of taking the entire thing out to access that one actuator? Anyone know a trick or easier way to do this? All the other doors I can see seem to work as designed. Any ideas would help so I am not going in blind. My first time doing this and any help is much appreciated! Been quietly reading on here a few months, just got the truck home early September.
 

75gmck25

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Bruce
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1975
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K25 Camper Special TH350 NP203
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5.7
That actuator on the back is hard to reach with your hand, and IIRC, the plenum has to come out to remove it. However, you should be able to reach the lines after you remove the glove compartment and the vertical plastic plenum piece behind it.

I also think that on my truck it’s the one actuator that has two vacuum lines. That dual feed allows the system to move the door in the plenum to closed, open, or halfway in between.
 

duece1951

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Fort Myers, FL
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thomas
Truck Year
1984
Truck Model
GMC C1500
Engine Size
305
So I need to remove the entire box to get at it well. I have all the other vent plumbing out to see them move and clean it in case there was stuff in there. Hornets nest and glass. Could something be bent inside?
 

duece1951

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Location
Fort Myers, FL
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thomas
Truck Year
1984
Truck Model
GMC C1500
Engine Size
305
My dash vet door only closes to about an inch and a half. Can hear a vacuum leak from the back. That why I asked if there was an east way. Not sure if that it but the entire dash is apart so need to address it now instead of doing this twice.
 

sidschev

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Arkansas
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sidney
Truck Year
1984
Truck Model
c1500
Engine Size
350
check for rats nest ect too........
 

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