On a '78 truck is it possible for the water (heater) valve to go beyond closed and actually open up again?
The cable popped off mine and I thought I had closed it by hand but the inside of the truck was still overly warm compared to outside air. Yes, I had the fresh air door in the kick panel open.
Which way is closed? All the way forward or all the way back toward the firewall? I hate working on this type of problem with only one set of eyes.