Last sunday my wife and I left town for a week's camping. On the way down the a/c was barely cool to not cooling even on max a/c while at cruising speed. When we arrived at our destination I made an appointment with the local Ford dealer for a/c service. The technician told me that the a/c pressure was exactly where it should be and even had another tech look at it. He checked the condenser coil and found it clean. Some years ago another member posted that even on a/c hot engine coolant still flowed through the heated core adding additional heat load. He had a fix that involved a vacuum operated valve from some other vehicle and posted instructions on how to hook up the vacuum so that when a/c was selected vacuum was routed to the valve and closed it so that no hot coolant flowed through the heater core. I did that some years ago after reading his fix. I have yet to check the operation of the valve to make sure that it in fact closing when a/c is selected. Does anyone remember that thread in case I have to replace the valve? I have no idea what vehicle that valve was for.
I've checked the compressor clutch clearance and it's good. I've wrapped my 4" exhaust with header wrap as far up the downpipe as I could to the rear of the cab.(I have the 7.3 diesel) to further reduce the heat load. Does anyone have any suggestion as to what I should check next? The a/c should do better than it is. The return trip weather was cooler but I had to keep the dial on max a/c just to keep from sweating!! I'm considering a thermal/sound barrier but am concerned about the mastic adhesive backing melting where the floorboard sits above the exhaust. Any information about this issue would be appreciated.