I installed two valves and it helped alot but I still get some warm air in the corkpit with the heater off, cause with the ign switch on the fan motor still runs with the fan switch off, has something to do with the Astro ventalation set up ,so now what I do during the summer is close the valves and disconect the fan ground lead so that the fan doesn't run, I don't run my AC cause it throws compressor oil, even when I replaced the seal, long ago I read somewhere here that you could disconnect a brown wirer I believe at the AC blower motor cut out relay or blower motor risistor I can't remember or find it again, but it kills the  the low speed on the blower motor but it still allows med and high to work, I'd post photos of my valve set up but don't have a clue on how to do it anips2009-06-23 18:50:19

Just for info sake I went to napa this morning to get my brake rotors (another project) the parts guy found me avacum of control vale that is for 3/4 in hose. so I had him order it for me and I will install and see how it works.

I totally agree with Joel. If you want to shut off heat, ya might as well do it completly with bypass connector. With my 71 its easy, as the heater hoses are right behind the side grill. You can get hose reducers, 5/8" to 3/4" at any auto store. I know because I order them 2 doz. at a time. As far as vacuum control valves,  iffin they worked you wouldn't have this problem in the first place. With manual valves your only gonna shut off part of the heat, not all of it as previously mentioned.