Ventilation System

While installing a new stereo in my '76 Suburban I had the dash apart, and decided to seal up the ventilation system for the heat/AC system. It was hard to beleive how many HUGE leaks there were in the system, some of which had to have been there since it was new. For instance, the vents on the dash were about 1/4"-1/2" wider then the outlets from the distribution boxes. The line to the defroster was about 1/2" from the defroster ducts. I have resealed and taped all the ducts and I can't beleive the difference...I can really feel the air moving now. It appeared that the previous owner had taped some of these leaks many years ago, but the duct tape he used was totally deteriorated. Also, the line from the distribution box to the far passenger vent was totally disintegrated...I replaced it with a 3" aluminum clothes dryer vent...should outlast the rest of the truck.
Anyway, if you are having problems getting heat, A/C or defrost air you might want to disassemble the dash and see if you have the same problems.
I had considered doing the same on my truck, too. With the selector in the VENT position and the fan on HI, I feel more air coming through the "character" holes (can't call them rust holes - Fords rust - Chevy's have character!) than I do through the vents. Defrost isn't quite so bad - I can feel air moving from several inches away on that setting.

The only problem with taking my dash apart is that I always, no matter how well I keep track of things, have three or four screws left over. So I wait until I have three or four things I need to do behind the dash before I pull it apart. So far my "to do" list consists of replacing the fuel gage, sealing those air ducts, and getting the stereo rewired and working. I'm waiting for a light to burn out before I tear into that dash again.

Good luck to anyone with dashboard luck like I have!!


mike reeh

Senior Member
Interesting you mention it, a few months ago, it dawned on me to do the exact same thing.. Ive had the dash apart a few times over the years and I have seen the huge gaps & holes in the air ducting.. I figured Id just wait until I swapped the cab over to the new frame, OR until summer rolls around again, which ever comes first..

This brings up another point.. The vacuum line that the vent system gets it vacuum from, in the engine compartment is completely toast.. Its a wierd little line too, Im not 100% sure how Im going to go about fixing it.. anyone had to fix theirs? Its a small, like 1/8" or possibly smaller like 3/32" line, not rubber but more like a plastic.. I havent investigated it to a great degree yet, but I know it aint gonna be a real simple fix.. any suggestions would be great.

Jeffs classics: Ive also heard that in order to help air flow, and lower the temperature of MAX AC, its good to clean out the cowl vent, and even the inside of the AC box.. leaves and other debris have a tendency to build up after 20-30 years..

One last thing, my all original AC setup works pretty good but the hoses leak.. mainly the low-side hoses.. Any one know of a good place to order pre-made replacements? Everyone I talk to says places will make them to fit, while you wait, and its very cheap, but maybe theres a better way... Been a few months since Ive worked on the AC system so things are a little sketchy in my head, but there is this one hose that connects to the AC compressor which is attached to the aluminum manifold on the compressor itself.. I think its crimped on, in other words it doesnt unscrew.. how do they replace that one??

whew sorry for the long post :) hopefully some of my questions will be answered...

mike reeh
The vacuum hose that you need to replace should be available through the dealer, or you can get a comparable (in function) piece at the local parts house. I don't know why the materials are different, I know what you mean about it being shiny and plasticy.
The hoses to your A/C are bolted onto the back of the compressor at the manifold. You have to buy the hose as an assembly, and they should be available at the dealer or most auto parts stores. CarQuest auto parts stores use Gates and Goodyear rubber goods, I would buy one from them even thought they tend to be a little higher.All the hoses on my '76 are new so I haven't had to check availability on them. Depending on what year truck you have your A/C hose system may be different. There was a change-over in '77, the new '77+ style is a better system, but I am not familiar with it.
I didn't clean out the A/C box because it appears that the evaporator core was recently replaced, and I assume that they cleaned the junk out of it while they were in there. I just bought this Suburban 3 months ago so I haven't really run the A/C much, but it seems to work great, even the rear unit.
Just hit a wrecking yard,and grab some plastic vacuum line off another vehicle.Most 90 and newer vehicles use this extensivly.Cut the longest piece you can find,and then patch it in to your system with little pieces of 5/32" vaccum line.You could even replace the whole line with rubber if you wish,it will just be harder to get through into the passanger compartment.As far as AC hoses go,ask at the parts store if the hoses are R134A compatable,as the old R12 is now obsolete.Replace all the hoses with R134A type,including "o"rings,and the reciever dryer,and then have the system charged with R134A.It's much cheaper and more readily available.You can also get at 99% of the ductwork through the glovebox opening and from under the dash,and taping it all up makes a huge difference.A higher speed blower motor (ie:from a newer ford),will also help speed up the airflow.

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