I am convinced that regardless of the position of that little wheel, the heat is on. I'm pretty sure that hot water is flowing through the heater core at all times. What's the deal? The only thing worse than a Corvette trailing arm is the its heater core. :mad

Bubba fixes will be considered...

 

It does get warm doesn't it. I, like others have added a hot water valve. And it does help, amongst other things. There have been numerous threads regarding this. Do a search to get the different opinions.

 

Glad to see one more 74 around! :D

If you don't have AC then you're right: the hot water is passing through the heater core all the time. The only thing that happens as you turn that wheel is you open or close a door which directs the air to or away from the heater core. The A/C cars have a vacuum operated shut off valve which stops the water flow, but I believe that only happens when the AC is set to "max".

The solution is to cut the hose that goes from the manifold to the heater core and insert a manual operated valve. It's a 5 minute fix, and it really makes a lot of difference!

Hope this helps...

-Pedro

 

Thanks for the replies.

The shut-off value sounds like the answer. My 74 did have AC, but it was carefully removed :smash: and placed in a milk crate.

Another thread mentioned the cable may not be closing the door completely. How can I check this?

 

Jack,

Look under the passenger side dash, and as you turn that wheel you'll see a cable moving a lever, which opens/closes the door. Turn the wheel all the way to the "COLD" side, and then see if you can move the lever any further with your hands. If so, you'll need to adjust it. On the non-AC heater box this is done by loosening a bracket that holds the cable, and moving it until you get that door to close completely.

-Pedro

 

74Jack;

Realistically, the only way to check it out is to do what I just did tonight: Remove the gauge cluster and the passenger-side dash panel and take a close look. It didn't take long to find the problem, but I haven't decided yet what's the best way to fix it. There's a small plastic attachment piece that one of the control cables attaches to and it's broken. The upshot is that the cable no longer operates the door, so hot air from the heater core continually flows into the cabin. If push comes to shove, I think I can fabricate the piece I need. I'd be very surprised if I could ever find an OEM replacement. By the way, on my car, a '73, I've never found any evidence of the hot water control valve that is so often referenced in threads about this problem. It's also not shown in my Assembly Instruction Manual (if you don't have an AIM for your car yet, get it as soon as you possibly can, you'll be lost without it). I'm not saying the valve doesn't exist, as a matter of fact, somone posted a picture of one not long ago, I'm just saying I'm not certain about whether or not all C3s have the valve. My car is also an air car from which the components have been removed. I believe that the heat problem can be solved without inserting a valve in the heater hose that doesn't belong there. I may be wrong. But one way or the other, it'll be learning experience and that's a part of the enjoyment for me. Taking the dash apart also gives me the chance to test all the bulbs and fix rattles and repair loose grounds and just generally push back the forces of entropy that slowly but surely take over if you don't dig into the car once in a while.

 

I have a 72 roadster with a/c. 72 was not equipped with the valve from factory. 68 to 71 and 73 to 81 had the valves from what I can find out. The valve is located on the passenger side near the expansion valve for the a/c. It can be accessed throught the side vent or from under the right fender

 

I have been using a 75 Convertible as a daily driver for 20 years. I had the same problem of heat passing into the passenger compartment. The only way I could get it to stop was to adjust the left wheel to "Heat" and the right wheel to "Cold
It works for me! :cool: