OK,I have a 1989 RS convertible,I have been working on my a/c controls and have had a problem with adjusting the vents,it would work on the defrost only and will produce a major vacuum leak when you change the temp selector from cold to warm.Now I have attached a photo and I have replaced the circular control valve today and it will adjust to all the different vent locations,but only when in the cold position It still leaks from the vacuum valve on the left,the one with two vacuum lines.It is not available from GM anymore.Can this be purchased elsewhere? Will that even fix my problem?

 

Are you sure the vacuum leak is under the dash? Is the water control valve still hooked up under the hood? When you switch from hot/cold it stops the flow of water to the heatercore. Just a guess, but if that vacuum line under the hood is just open that'd create a vacuum leak.

 

Well I have had the unit in my hands with the car running and it clearly comes from the valve that I have described,but I will check under the hood also.
Thanks for the help.

 

You were right! the water control valve has no vacuum line to it None in sight,Do you know where it comes through the firewall at?

 

Comes out the firewall on the pass side between the heater blower housing and the block - same exit as the wires that run the heater blower motor. There will be 2 vacuum lines there - one runs IN from the vacuum ball (driver side under front headlight), the other runs OUT to the heater diverter valve.

 

AHHHH,,Ok I have only one line from that area,other must be cut off behind the firewall.I have one coming from the vacuum ball over to the distributer area and teeing off to a vacuum tee in top if the intake manifold and blocked off from there.So I surmise that if I can locate the other vacuum line behind the firewall and connect it ti the blocked vacuum line mentioned,it should work! Thanks again for all your help<I will keep you posted.