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Topic: 1978 AC from scratch

in Forum: C3 Cooling and Heating Systems


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1978 AC from scratch (1/11)
 6/24/15 10:41pm
1978BackToLife
Former Member

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Burbank, CA - USA

Vette(s):
1978 Corvette Candy Red


Joined: 6/24/2015
Posts: 1

Hi all, first time poster... began searching for a while on the forum but thought I could make a new post.  Younger kid that just acquired my first corvette with decent understanding of cars.  Didn't have the budget for a big block, but got a great deal on a 1978 standard model with AC.  It's extremely hot now in LA in the summer and I'm looking to try to bring the AC back to life.  With R12 being impossible to find, my goal is to fix what's broken and convert to 134.  Much thanks in advance for any guidance.

I'm wondering if there is a start to finish step-by-step guide, post or other doc on late C3 Corvette AC systems?  Is there a suggested reference guide for wiring, diagrams, how to test, youtube series etc (locate an original shop manual or Haynes, etc) I'd love to take it into a shop but I just don't have the budget to turn it over to someone.  I do have all the time in the world, and the budget for parts.

As for my exact issue, here's what I've noticed from a system that's probably been non-op for a while.  What do you recommend starting with?

1) Belt missing for compressor (if I just put one on, any potential to damage compressor etc?)
2) Compressor does spin freely by hand if that matters with little resistance
3) Compressor wiring is disconnected, and harness clip is broken - not sure which wire attaches where
4) I see the heater core has been rerouted, do the systems work in tandem so that the heater core has to function for the AC to function?
5) Will surely need to test other AC components, just not sure how and in which order

in the cabin:
6) Fan blower works on all speeds
7) Stuck on floor setting, can't get to move to panel vents so I assume it's a vacuum problem - any diagrams for vacuum lines leading off the climate control switch?
8) cleaned contacts on switch and reassembled, still stuck on floor setting

Thanks so much for any help, trying to get my first vette going :)


(modified life-sized image to link-aapple)









|UPDATED|6/24/2015 7:41:58 PM (AZT)|/UPDATED|
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Re: 1978 AC from scratch (2/11)
 6/24/15 6:08pm
dwa175
Former Member

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leesburg, FL - USA

Vette(s):
1979 coupe and now 2007 c-6


Joined: 7/19/2014
Posts: 195

well welcome a board,you got yours full,it tells me some one didn't know what they where doing. frist ,changing to  r-134 is easy  in conn to install you have to have lincese[spelled wrong]   vaccum hose  hook up ,belt put on ,does fan work at all speeds or just high.  hot up see if anything works the people her will help you  with you will get it fixed  at what cost I do not know  keep us posted   do not try to cut corners it will only cost you more   good luck   dwaBeer
Re: 1978 AC from scratch (3/11)
 6/26/15 12:41pm
tb2k82ceLifetime Member
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Lemon Grove, CA - USA

Vette(s):
1982 C3 Collectors Edition 44000 miles, sat in the sun most of its life, My wife purchased it for me for Father's Day in 2007 from her girlfriend that had it for 19 years. It is on the road again. I'm retired but it is now my daily driver.


Joined: 10/17/2007
Posts: 2041

If the heater was bypassed I would guess that it was not working and I would think about fixing that also.  It will mean taking the dash out I believe. That may make it a non-starter if the dash is old.  I do not believe you can put the twist on the dash to get it out without breaking something.  If however you can it would be worth the trouble.  Also if you take it out do not forget to replace all of the lights in the dash. 

I has the same problem with mine but I had purchased R12 the week before it became not available so I had some. 

Your question on if anyone had a drawing.  I made one so that I could better understand the system.  I will try to attach it but if that does not work send me an email and I will send it to you or anyone else that wants it.  gilbert@ghmail.net  note it is ghmail.net not gmail.com.  It may be more readable and printable if I sent it to you as a file  /member_uploads/10901_11000/10990/82-Heater-AC-control-system-2.jpg.

I also have attached the center gauge panel circuit board drawing  /member_uploads/10901_11000/10990/Gage-Consule.jpg

Vacuum hose layout general  /member_uploads/10901_11000/10990/C3-Vacuum-Hose-Layout.jpg

Headlight Vacuum hose layout 80-82  /member_uploads/10901_11000/10990/1980-1982-Headlight-Hose-Vacuum-Diagram.jpg

If I needed I can send any of these as a pdf via email they all started out as MS Visio drawings.  I believe they are 100% correct as I used them all to work on my car but if there is a mistake please let me know. 











|UPDATED|6/26/2015 9:41:01 AM (AZT)|/UPDATED|
Re: 1978 AC from scratch (4/11)
 6/25/15 2:53pm
kstyerLifetime Member
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CUYAHOGA FALLS, OH - USA

Vette(s):
1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!


Joined: 12/2/2003
Posts: 6424

All good information above.
An alternative is to replace the system with an aftermarket from someone like Auto Air.  Might be more to that name.  They make A/C systems for older cars, using new components and operating on R134a.
You can also get a conversion kit to change it to 134a.   As a start you may want to go to a parts store, AutoZone etc, and get the adaptors to connect 134a to a older r12 system.  Then you can put it under vacuum and perhaps add a bit and see what happens.  Then you can leak and operation check. 
If you find it works, you will expect a bit less cooling with the newer refrigerant, but it may be enough to cool the car and make you happy.
Re: 1978 AC from scratch (5/11)
 7/4/15 12:56am
73shark
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


Joined: 7/9/2003
Posts: 864

Despite what you may have heard, R134a doesn't work very well in an R12 system. To be effective you need a bigger condenser and you would have to get rid of all of the existing oil in the system. Also the O-rings would need to be changed to be compatible with the Ru134a oil.

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1973 L-82 4 spd

Re: 1978 AC from scratch (6/11)
 7/10/15 12:20pm
snake97
Former Member

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Metairie, LA - USA

Vette(s):
1979 Black, Oyster interior purchased in March 1980


Joined: 7/7/2013
Posts: 24

  Had similar issue with my 79. A/c hadn't worked in years. Wanted to keep car as original as possible, but, I try to consider all options. Repair what you have and hope that it works. Rebuilding what you have and replacing parts will cost something. Face it , after 37 years things wear out or go bad, or deteriorate. The freon is different and retro fitting an old system may work, but how good and for how long before something else needs to be replaced or repaired? A new system will cost a bit upfront, but should last hopefully for a long time. But you are losing some of your car's originality. I opted for the latter. An upgraded system, I feel, won't take away that much from the car. I still have the old system put away. Over the past few years I've had to replace just about everything on the car, so I would have to consider my car a restored car not a survivor. I drive my car regularly so I want it dependable. I purchased a complete system from Classic Auto Air last summer. I figured I could have gotten my old system working for half the price, but how good and for how long would it last. This has been my experience with my Corvette. You try and cut a corner to save a little money and time but it bites you on your butt quickly. Several jobs I've done hoping I could get by cost me in the long run by having to go back redo something that you did. {front and rear suspension parts that I felt were still good enough]. My advice is to save a little longer and replace everything once and be done with it and you will have something dependable. Classic Auto Air was a pretty easy install. I've never done anything to an a/c before and I really didn't fully understand them until I replaced mine. The people at Classic were very helpful and after I installed my system, I feel pretty knowledgeable about a/c's. No expert, but I understand them. Just my thoughts from my experiences.
Re: 1978 AC from scratch (7/11)
 7/10/15 6:22pm
dwa175
Former Member

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leesburg, FL - USA

Vette(s):
1979 coupe and now 2007 c-6


Joined: 7/19/2014
Posts: 195

remember cheap cost more   dwaBeer
Re: 1978 AC from scratch (8/11)
 7/11/15 3:11pm
dwa175
Former Member

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leesburg, FL - USA

Vette(s):
1979 coupe and now 2007 c-6


Joined: 7/19/2014
Posts: 195

tb2k  I just printed your schematic for heater control vacuum.   hers to problem for anybody,the car ac worked always,ihave had car 20 years,redone hole car 2 years ago no problems,i had to replace heater/ac fan during winter  alls ok   I do not what to do another.  giving car shake down drive,no ac,ac comp don't ingage check fuses blown never good,replace c/b  know clutch works but nothing happens fan blow heat only no ac nothing comes out of top vents only floor,no defrost no nothing  I have not done any work on this car,i replace seats,door panels,steering wheel[its lost in shipping]  I don't know wear to start vacuum seems to be right,i need input from you fellas opps and woman   dwaBeer
Re: 1978 AC from scratch (9/11)
 7/19/15 11:03am
dwa175
Former Member

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leesburg, FL - USA

Vette(s):
1979 coupe and now 2007 c-6


Joined: 7/19/2014
Posts: 195

good news  traced ac/heater problem to broken arm on control unit in dash,removed controller,all this was in a1/2 hr by removing consol side panels,new on the way.note  this car is the that keeps takinging I long ago used more money than I can count but who counting    my wife    any way I may be on the road this year its been a long road  3 years  I am 66  I would like to drive it one more time    remember the wave   thanks   dwaBeer
Re: 1978 AC from scratch (10/11)
 7/25/15 9:39am
SSc3-1972
Former Member

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Sarasota, FL - USA

Vette(s):
1972 C3 work in progress


Joined: 7/24/2015
Posts: 2

Vintage Air makes a kit to modernize the older systems. You can convert an R-12 system to R134 but it won't get that cold. It's a little pricey but well worth the money if you're keeping the car long term.

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Re: 1978 AC from scratch (11/11)
 8/7/15 1:55pm
kbrin
Limited Member
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coral springs, FL - USA

Vette(s):
81 beauty all original (not anymore!!) Its more fun now!


Joined: 3/25/2014
Posts: 71

If you have the budget put Vintage air in and be HAPPY! did it to my 81 and its really perfect.
I own an AC contracting co. so i am really picky about this stuff. I must say that I am really pleasantly surprised at the quality and operation. shop it at summit  ecklers CA etc or bring it to one of their authorized installers.
I did some mods like making a shorter glove box to fit the system and a few others and would be happy to share if you go this way.


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