I'm having issues with my a/c. When it works, it works pretty good. There's a lot of air to cool inside, but it does cool down. However, sometimes when I turn the a/c on, I get full heat. I'll turn the system off a time or two and back on and it will start cooling. Does this sound like my water control valve is sticking and might need replacement? I'm planning on changing the coolant before winter and that would be a good time to swap a new one in.

2004 Expedition NBX with regular heat and air.

 

To me it sounds like a blend door issue. Coolant flowing through the heater core will not cause full heat when the AC is running and the temperature selector is set to cold.

 

Got to poking around on the water valve and it's leaking internally. Sometimes the hot water is stopped and sometimes it's seeping pretty good. I'll replace it when I service the cooling system before winter rolls in.