[LBJ]

It's too late to take pics because I have already done the fix. The defrost problem on my 77 was due to the vac line INSIDE the plenum assembly under the dash being rotted away. You have to stand on your head to get to it. I used some silicone fuel tubing to replace that line with since it's something you don't want to do again. There is a vacuum actuator INSIDE that pulls the door closed for the defrost and releases for the other functions. Once you get a light in there, you can see where the actuator is and plan your attack from there. Some diassembly of the plenum chamber is required. I used some long nosed forceps to attach the line to the actuator. The other lines are pretty straight forward to get to. Start at the carb and go to the little accumulator ball on the firewall first. Then, the line goes thru the firewall to the various actuators. Some of the lines are plastic with little flexible nibs of clear tubing on the ends. The plastic line usually does not wear out, but it might get cut or crimped and need replacing. There is also a vacuum line going to the actuator right in front of and under the windshield wipers on the passenger side (under that plastic screen). Check that too for loss of vacuum.

My system now works like brand new, including fixing the problem of feeling like the heater is on all the time. I am very satisfied now.