So I have a 2001 Montero LTD, and the car heats up fine no problems. Now when I select for heat to come out no matter whether its on the dash, floor or vents, I get a cool/warm air not full heat. I have changed the Thermostat already. No problems with heater core because its not leaking not leaks on carpet or anything. I'm thinking the valve to fully open for the hot water to go into heater core isn't working but does anyone know how I could check that? Has anyone had this issue before? Does anyone know where I can find that valve?

Thank You

Lem