for some reason my heater wont turn off. i have tryed evrything to try and stop it. I've talked to several people and they all said that its the heater control valve is stuck. well i try'd to find it and i cant. my haynes guide said that it should be connected hoses going to the heater core. well its not ther the book even showed a picture. i need help and advice cause it gets extremely hot in my truck.