I have a 1978 coupe with an L48 engine. The car is equiped with AC although I'm currently waiting for a new main line at this time. I'm currently experiencing heat in the cockpit with the heater controls shut off. I'v replaced the vacuum diaghram in the controller as well as the shut off valve under the hood. I've also checked for vacuum at the valve and there seems to some vacuum there. I'm beginning to think its just engine and catalytic converter heat coming into the cockpit, but I'm not sure, does any one have any ideas with similar experiences

Bob, welcome to the registry!! You can install manual heater hose shut offs which stops the water from coming into the heater core. Check out this link for pics of what it will look like
Chris
http://forums.corvetteforum.com/zerothread?id=281931

It's not just you, Bob. It is a common problem. There has been a lot of discussion on the registry lately about this problem. If you do a search in this forum on heater or heat, you will find the threads and the proposed fixes.

I gotta tell ya...now that my A/C is working...the heat from the floor is hardly noticable!

|QUOTE|Adam said: I gotta tell ya...now that my A/C is working...the heat from the floor is hardly noticable! |/QUOTE|
Thanks for rubbing that in Adam. the one C3 owner with a working air conditioning system

|QUOTE|82dukman said: |Thanks for rubbing that in Adam. the one C3 owner with a working air conditioning system |/QUOTE|

Don't be so jealous... it'll probably fail on my way to Bowling Green!

This seems to be a common problem from everything that I saw on the tagged forum with the C3's. I like the double valve idea for the summer when its hot, however, the I didn't care for the plumbing ball valves under the hood idea, I'm sure they work. There was a suggestion of a PEX valve from Lowe's, so I'll take a look at those the next time I'm over there. My new main AC line came in yesterday, so I'll install it Monday, hopefully its the right one this time. It will be nice to have the AC working again. I've not replaces the whole system, minus the evaporator and condensers. After all this, it had better not fail on my way to Bowling Green next June. I'm also going to put the heat sheild under the carpet in the car. Its availible from Eckler's and Corvette Central. Hopefully that will also help some. My goal is to shut off the heat from the cockpit and not have to go under the hood to turn on/off manual valves, but in a last resort I will. Thanks to everyone for all of the information, it is greatly appreciated.

Bob

You can buy both valves-3/4 and 5/8 online at auto parts giant. they are smaller and look like they belong there.

Stock heater control valves work. Some things to consider:
The rubber valve seat in the valve only lasts about 5-7 years, less if there is rust in your cooling system which clogs the seat and allows a constant flow.
A control valve requires 14-15 inches of vacuum to seat (new). Air diverter valves in the ducting require 7-12 inches to operate, less if the spring on the door is used, more if it is rusted.
Normal engines produce 17 inches of vacuum at idle, and about 20 inches at cruise. Big blocks run about 2 inches less. Big cams and poor tunes can decrease this number to 12 inches at idle, and 0 inches at heavy accelleration.
Most problems (90%) I have encountered in 15 years of corvette restorations with floor heat are not with the valve itself, but with poor vacuum to the valve, coming from: bad control valves in the center console, loose vacuum hose ends at penetrations and connections, bad check valves leading to vacuum reservoirs, and disconnected lines at diverter valves.
It is a desire for most owners to stay with the original engineering of a corvette. Brass elbows and toilet valves under the hood are unsightly and distract from what otherwise may be a great engine compartment. I recommend you check the entire vacuum sysytem, preferably with a hand held pump, and a flashlight and inspection mirror. I think you will find 20+ year old rubber hoses are causing your hot floor.
K & M Restorations.

Well I got rid of the the heater core all together by unhooking the heater hoses and i still have a lot of heat in the car... NOW WHAT?