I got my 2004 less than two months ago. A few days ago, I noticed that air wasn't flowing out of the vents very well, particularly the center and left vents. With huge thanks to this forum, I searched for the problem and found that it was likely a vacuum hose leak. After spending a couple of hours searching for the leak, I got lucky and found a tear in the hose right outside the passenger firewall, and repaired it. As far as i can tell, everything works fine now. Had the leak been anywhere else, I would have probably never found it (car would have gone to the dealer).

That brings me to my main point: Why did Chevy design an HVAC system that uses a vacuum hose? I'm certainly no expert, but I'm pretty sure our other cars (Toyota and Lexus) both use electric motors INSTEAD of a vacuum hose to control the vents. Had the Corvette had an electric vent control system, I would have never had to deal with a stupid leaking vacuum hose. With well over 10 feet of hose, all of it very hard to access, just one little leak can screw up the system, and the leak is extremely had to find. I know the likely reason that Chevy designed the system this way was cost (I'm sure the vacuum system is cheaper than electric motors), but the vacuum system is a terrible idea (imo) when there are much better systems available.

 

GM's have used engine vacuum for 50 years-get used to it. It's simple and it works. My 69' had vacuum actuated headlight, wiper door, rear vent system AND HVAC. If you think the current system is complicated with 1 hose, you should troubleshoot an early C3.

 

I'm not negating that it works (that is, WHEN it is working). The 'simple' aspect of the system is debatable. It is certainly not simple to fix if something goes wrong. I would much prefer a couple of electric motors to a bunch of vacuum hoses behind the dash. Electric motors can't get kinked, cracked, severed, torn, etc. If one breaks (which is barely ever), you just replace it. There is no guessing where it is broken, etc.

 

Vacuum is just as easy (or easier) to diagnose, all you need a handheld vacuum pump w/ guage on it instead of a VOM. Very SIMPLE and you'll never fry a circuit or pop a fuse with vacuum. Simple-Simple, even a CAVEMAN can do it.

 

my 78 has the same with the exception of the windshield wiper configuration (thank goodness, lol) the other advantage the 78 had over some of the earlier C3 models is that it only used one regulator valve for the headlights instead of 2 that were used earlier. when it goes south it's a real thrill trouble shooting and repairing it, LMAO!! i know because i've had to do it twice in the last 5 years, lol! like the man said, it's a GM characteristic, you just have to get used to it.

 

The trick to diagnosing these systems is the handheld vacuum pump with guage. You can also use it to bleed brakes.