2003 Ford Explorer

Heater problem
2003 Ford Explorer 6 cyl Four Wheel Drive Automatic 40,000 miles

When I turn the heater on it makes a " clicking" noise. When I turn the knob to cool, the noise stops and when I go back to heat it starts again. The noise even continues after turning the heater off. I also noticed the air only comes out the window vent no matter what vent setting it's on or if it's hot or cold air. I unplugged the blower fan and it still makes the noise when I turn the heater on. I want to say it almost sounds like something is trying to click on or off, but it's sticking. Any info or guesses would be appreciated. Thanks.
October 22, 2008.

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