i am working on a 77 240 se i am having the same symptons as you are. i posted alomost the same as you and got no results. BUT, i discovered a box /valve on the passenger side by the firewall has a bunch of wire looms and about 20 vac hoses coming out of it. it was so corroded and froze up that was junk. it has a rotary vac valve in it and a bunch of gears like a clock ,they work the blend air doors vor the vent a and also the hot water . the water valve is the bottom half. i have one ordered for this one. better be sitting down when you get the price. hope this helps .....digger