Explorer heater not working

[jollygrngiant]

My wife has an '03 explorer, and just recently her heater has stopped working. Every time you go and turn the thermostat to the warm side, somewhere back in the dash you hear a clicking sound. So right now the only thing that works is the cool side. I know I have to take apart the dash to get behind it and try to find out where the noise is coming from, but what I don't know is what to look for. It might be the fan motor itself......I don't know. Any ideas or pointers???
Thanks
Brian