When the eng is cold the a/c blows cold but once the eng warms up it blows hot. I checked the heater core bypass door actuator and it works. My question is could the water temp control valve be the culprit?

Yes. It could. Be sure the temp control move the valve shut off lever if it has one.

Pinch off the heater core hose and see if that makes a difference. Also, if the AC is working all the time, the tail pipe ( by the expansion valve ) will be cold all the time.