Welcome to the engineering marvel of the C-3`s. No the HVAC control is not impressive, I replaced my 77 controller a few years back The old one completely fell apart and the temp lever broke in half. The new one is flexy, 77 was the first year for that controller. It takes time to find the sweet spot on the controls.you might try hooking up your vacuum pump to that valve, I think that spring is strong to compensate for the vacuum. play with it. The air volume is not great even on its best day, make sure the max vent servo and door is working right. I hope you have the right fan and motor, It will make a difference if the engine is running, more voltage faster fan. If you want to see how much crap is inside your hvac case in the bottom. you can pull the fan speed resistors from the top of the case, (two screws) and see the bottom. debree coats the front of the evaporator. and slows down air flow, might be a good time to vacuum and blow out the vents. (if you haven`t already) 7 mpg thats impressive, Are you smelling gas when you park? ( I had to replace my fuel pump return line, it cracked and had a strong smell in the gerage leaked all over the top of the fuel tank) Hopefully your fuel is not more than 10 percent ethenol. check your engine oil to be sure that you don`t have a fuel pump leaking into the engine oil. Cheap made gas burns faster for some reason . Good luck. Keep us posted

 

I read an article years ago that said you could use a C4 fan to move a greater volume of air. It did require a spacer between the fan and the ductwork.

 

Mr. 73 shark I saw the article about C-3 fan performance you were referring to I believe, It was an article on Digatal Corvette forums on 1/3/2014. Interesting article.

 

Good find. I'll have to look it up again and print it out. Since I currently have the engine out, it would be a good time to do this.

 

Found a fan and motor on rockauto, a/c delco for $38. I can`t find a ready made 1" spacer, but amazon had 1"x12"x12" plastic for about $25. I will make a spacer. I think it`s worth a try, thanks for peeking my interest..

 

You may have to post a link to that particular thread on Digital Corvettes as they changed their password requirements since the last time I was on there which was a lot of years ago. I asked for a new password.

I seem to remember from when I read the article that they used a piece of 3/4" plywood for the spacer. If I'm looking at this right, the extra portion of the C4 fan will actually be inside the spacer which will limit its effectiveness to increase air flow.

Let us know how it works out for you when you get it done.

 

There was no password, it was an old story I ran across. I will go back and see how i found it. when i saw the story i remembered what you said about the C-5 fan and motor. this guy was using two pieces of 1/2" plywood glued together to make 1" spacer. then he mixed up some fiberglass resion to coat the wood for water proofing. I will search for the post.

 

I found it by google search Poor C-3 Air flow-Blower Motor. And it took me to Digital Corvette story. No log in No password, I did get the date wrong it was jun 3 2014 not jan (reading has always been hard)

C-3 hvac modifications

 

Thanks, found it.

 

I see that he used a C5 blower. Is that what you got?