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77 Chevy 1/2ton heater vent linkage
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okmatthew
New User
Jun 11, 2008, 7:16 AM
Post #1 of 6
(1842 views)
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77 Chevy 1/2ton heater vent linkage
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77 Chevy 1/2ton 350CI heater vent linkage issues
I'm disabled Viet Nam era Vet. I need to know how to fix the linkage on the vent controls so the air will go throught the vents intead of just on the floor. an exploded view would be helpful or someone with knowledge. Thanks!
Matthew Dunham
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jun 11, 2008, 6:11 PM
Post #2 of 6
(1839 views)
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Re: 77 Chevy 1/2ton heater vent linkage
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Hi Matthew,
First - is this a non A/C truck from new that you know of?
I don't have exploded views either way but a not A/C one should be simple and either are cables right from dash to a door in the distribution box. Does the selecter just feel disconnected at the controls or some noise going on out of sight?
The vintage of this should use fairly simple stuff common to many GM vehicles for parts or perhaps hardware store items.
Depending on what's broken it may be possible to move the diverter door by hand and leave it in the mode you want for a time until parts are available??
T
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okmatthew
New User
Jun 11, 2008, 7:05 PM
Post #3 of 6
(1837 views)
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Re: 77 Chevy 1/2ton heater vent linkage
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Hi and thanks for your reply!
I don't have anything to compare the 'feel' of the movement to at present but everything seems to move without difficulty. The controls are very simple in that the bottom controls the temp from cold to hot and the top controls the A/C Max Normal Bidirectional Vent and Defrost. When I put the control in the Max and Normal A/C position the Air Conditioner turns on and when it is in another position I get Heat when I adjust the bottom control toward Heat. There is a nominal amount of air flow from the defrost as well as the Dash Board vents but the bulk of the air flow is on the floor. I'm the type that likes to feel it in my face cold or hot ,so your suggestion "it may be possible to move the diverter door by hand" seems to be the most appropriate at the present. I am disabled with lower back problems which is why I was asking for an exploded view of the system so I would have the correct target in mind when I struglled down there to locate the problem. You seem knowledge able enough to be able to describe to me what I am looking for so i'd be willing to learn from your experience and see if I could adjust the diverter door by hand and while there check the movement of the cabling. So do you think you can describe this 77 Chevy 1/2t PU 'Diverter Door' in a way a novice like me can locate it, what it looks like, and what to do when I find it?
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okmatthew
New User
Jun 11, 2008, 7:37 PM
Post #4 of 6
(1836 views)
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Re: 77 Chevy 1/2ton heater vent linkage
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Oh Ya, I didn't quite understand your question 'First - is this a non A/C truck from new that you know of?'. I assumed you were asking if it was factory air? Well That May Be Not What You Were Asking... anyway, to finish your knowledge of what I've done so far Short answer: Factory A/C - It does keep the freon in it and it does cool) Long Answer: it is in a truck that originally had Factory a/c and I bought the truck after the compressor and a/c hoses had been removed. I have another 77 with a Very Loud Knock (Thrown Rod? I'm Guessing) (This is a 78 and I said it was a 77 but they are identical) anyway a couple of years ago I upgraded the system to 134a by replaced the part where the freon on goes in. A canister looking thing with an inlet and a hose, plus all the other hoses plus the ?orifice? (a small inline filter with a fine screen) which I inspected very well before reassembly and replaced all the rubber 'O' rings and installed a new compressor, plus I blew out all the matter within the system (mostly oil), put a vacuum on it for more than 30 min, put in some freon then 8oz of oil then more freon using a gauge to not exceed the yellow section.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jun 11, 2008, 9:57 PM
Post #5 of 6
(1833 views)
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Re: 77 Chevy 1/2ton heater vent linkage
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Ok - slow down a second. This is a factory A/C system - doesn't matter if the thing makes cool air just that the whole system is different. I would bet most 77 Chev trucks didn't have air conditioning - trucks were just becoming universal transportation instead of just work vehicles.
No matter - the top selector I'm about certain is vacuum controls. As you move the lever along different holes line up and direct the vacuum to move the ducts for the assorted combinations. You have one that allows airflow to the floor that should be shut when asking for A/C that isn't completing the move of the duct. You may be able to see what moves at all on the plastic housing I'll name the distribution box and make it do functions moving it there.
At the age the vacuum operated things wear or the diaphragm at the distribution box is leaking OR the door is broken with perhaps pivots in the plastic worn - they work like a choke plate in a carb if you are familiar with those.
This truck is close to 32 years old and the book of possibilities is wide open. Common problems were vacuum leaks or disconnected line that feeds the vacuum to the whole control panel which should be a plastic ball underhood. That gets its vacuum from the intake manifold. If it changes any selection there is some vacuum working. The common failure with leaks was ducts would come to rest and stay at defrost only and NO air would come out the floor. More must be wrong with this one.
This is going to be near impossible for me to suggest what to do about this with the symptoms you described. If you can hear a hissing sound that doesn't quit that would be the place to look. If not it could be mechanically broken at vacuum actuator or a diverter door itself- stuck, broken or jammed up in the wrong postion.
Best I can say is you should hear vacuum hissing as you change selector from one to the next. If nothing then check that vacuum source is intact. There are vacuum actuators you should be able to see move or not and if line is hooked up or not.
Vacuum actuators look like this........
T
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okmatthew
New User
Jun 13, 2008, 8:56 AM
Post #6 of 6
(1826 views)
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Re: 77 Chevy 1/2ton heater vent linkage
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Ok thanks for your help.
The system is Factory Air and not an add on. It does not Hiss nor did the 77 which directed the flow as needed using the controls. I had two Lincolns and they hissed so I know the difference.
I'll search for a Chevy Truck Expert instead of an A/C expert able to help me understand the cable controls.
Thanks again for your help!
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