Heater Hose Question

[KellerMAC]

After my rebuild, I just recently recharged my factory AC unit in my 72 C10 and it blows cold but once the truck heats up, I am getting some hot air in my vents. I have a new heater control valve on the inner fender wall, but it seems to let hot water by. I installed a in-line cut-off valve and that cured the problem, but I don't like that solution. Why would the heater control valve not do it's job?

All comments welcomed.

Thanks

KellerMac