Hi Bill –
How you doing? I have a 1965 Lincoln Continental and the defrost will not work the heat vents and all work but the first time I took the dash apart the blower switch was fried and a little melted I replaced that and then found a vacuum leak I traced the leak to what I thought was the evaporator shutter actuator which I replaced checked the new/used one and it was leaking but it held vacuum fine when I installed it. Then I got a N.O.S. one and put it in checked it and everything was good so I put most of it back together and once all the vacuum lines were hooked up I checked the system and it was leaking again! And I checked the evap shutter actuator and it was leaking again. Do you have any ideas of what it could be or what to check, change or replace or guidance in the right direction?
Your statement “And I checked the evaporator shutter actuator and it was leaking again” suggests that you may be working with old and deteriorated vacuum actuators. Unfortunately it is entirely possible for even n.o.s. parts such as this to be aged and ready to fail when they are installed. This can happen with certain parts that are fifty years old and stored in all sorts of environments. In any case the best way to test and diagnose a/c-heat vacuum systems is with the use of a shop manual that has the ” correct vacuum schematics” shown and using a hand held vacuum pump as you may have been doing already. This manual will also show you the defrost duct work installation and the vacuum flow of the various switch positions. This way you can test the integrity of the vacuum switch and all of the vacuum components separately as well as determine if the vacuum hoses are routed correctly by color code etc. If required we have many parts available for your 65 Lincoln. Good luck and let us know how the repair goes.