1994 Lincoln Continental No Heat

I am working on a 94 continental, I replaced the radiator and the thermostat as well as some hoses because of a coolant leak in the radiator. It has no heat in the cab, I checked the supply line coming from the thermostat and it is hot but halfway to the firewall it encounters a valve and after the valve the line is cold. I was wondering if there is common problem with these valves or if there is perhaps a sensor I have overlooked. Thank you