Hi All. I have a 73 Roadster that I am finishing up and my vents are always letting in a little warm air (isn't everyone's?). I was thinking about putting in two manual valves in the heater hoses that go from and to the heater core to shut off any warm water which would allow warm air to leak in through the vents. I put a couple of pics online to see if I'm doing the right thing. Anything else I should do/know other than just cutting the two lines and putting in the valves? Thanks!

http://www.thestarkeys.org/vette/100_8856.jpg (hose 1 from manifold)
http://www.thestarkeys.org/vette/100_8857.jpg (hose 2 from water pump)
http://www.thestarkeys.org/vette/100_8858.jpg (hose 1 and 2 running along bottom where I'll put in the valves).

Hi MikeC3, looks like you have a good idea! I put a ball valve on the 5/8 line last year but the heat still came in after a while, just got the 3/4 shut off and will be installing that this week. Let's see if the A/C works any better with two valves, PG.

Here's the 5/8 one installed

That looks a lot cleaner than the gate valves I used. I've seen some vacuum operated dual valves but can't remember where. One of these days will have to look again.

Mike: The last two pics are the same. ;)

Hot Rod Air has vacuum operated valves with their kits. They may sell tham separately.

Frequently the foam rubber seals around the vent doors will deteriorate and allow air to enter the cabin even when they are closed, they may need replacing.

Thanks for the reply DV8, the only seals that I can confirm that are good is the one inside the right kick panel. I still have only the one ball valve shut off installed on the 5/8 heater hose. It works 100% and I had it in the off position today. I turned the thumb wheel to heat and got heat inside the car? Than I turned that thumb wheel to cold and turned the A/C thumb wheel to max A/C and got cool air. I'm don't understand how I could get hot air inside the car with the ball valve on off. I will install another ball valve on the 3/4 hose this week and see what happends then. I still have the R12 A/C system. I'll let you know what happends next.
Found this site www.corvetteforum.net/c3/zwede/71corvette/ac/retrofit.htm but I'm not sure if that is all the information that I need. Ever heard of this conversion, and does it work?
PS. Since pulling the A/C box is a major project I'm not going to change the seals until to heater core leaks. PG.

Hey PG. I put in both manual ball valves last week. I didn't want any hot water to seep back up the other hose so I completely blocked off the heater core. It was pretty warm out this weekend and got to go for a few rides and I'm extrememly pleased. There was no hot air coming from the vents at all. The air that did blow through was just about outside air temp.

I don't have my A/C connected since the compressor blew out, but when I do (next couple of weeks), I'm going with ES-12A. It's compatible with both R12 and 134 and is much colder plus a larger molecule. I've looked into it quite a bit for when I replace my compressor and it's definitely the way I'm going.

PG, I think the reason you need a valve in the return line is because of the heat conduction thru the water eventually heats up the water in the heater core.

Mike, what's the scoop on ES-12A? Never heard of it. I did hear that it was propane/butane based. Not sure would want a flammable gas under the hood. But it would make finding leaks easy. ;)

There is a definite difference with the heat coming from the vents after plugging both hoses. And, in the winter, I'll need to open the valves for heat, so it's perfect.

I found this link online:
http://autorefrigerants.com/co00033.htm

I also called and spoke with someone in length about ES-12 (or ES-12A) and I got quite the lesson in refrigerants. I also went to a swap meet and spoke with a local dealer. All I need now is the new compressor and belt, swap out my old compressor and load up with ES-12.

Hi MikeC3 et al: was ready to cut into my 3/4 hose and install the second ball valve when I realized that even though the ball valve says 3/4 the ends are only 5/8. Back at Lowes they don't have the right size so I'll try to get to HD tomorrow. Where did you get yours?
Thanks for the information on the ES-12, last time I paid about $65.00 a pound for R-12 and I'm not sure if there is anyone who has any. PG.

I got the 3/4" PEX ball valve for my 5/8 inch line which I bought off the shelf at Lowes. As for the 3/4" heater hose, I had to build my own ball valve (I bought the parts at Lowes as well since they don't carry a larger PEX one) using a 1/2" ball valve and then screwed in two brass pipe 1/2" MIP x 2" nipples in either end. I then clamped both down on the cut hoses and it works perfectly.

I need to pick up a new compressor and belt first and then add the ES-12. Any suggestions on where to pick up a compressor? At my local AutoZone, it's only $150 or so. I'll be clearing out my A/C lines to add just ES-12, but you can add it to your R12.

I googled on ES-12 last nite and found a ton of info. Also a place where you can get R-12. You used to have to have a license to buy R-12. Probably still do.

Anyway after reading all of the info, I'm not sure whether I'd use the ES-12 or not. I did buy a 30# bottle of R-12 right before they made you have a license to get it.

When I had to change out the compressor in my IROC-Z, I made a poor man's R-12 recycler by using an empty 20# R-12 bottle. I set it in a bucket of ice water and connected to the system. Since the pressure at 35* is a lot less than at 90*, the freon goes to the low temp. bottle. Surprisingly I managed to get almost all of it out of the car.

Hi again, thanks for the parts list, I try again at Lowe's.
AutoZone my other favorite place, lifetime warranty!
Thanks again, PG.