All Time Heat

My son's 99 Jimmy has excellent heat. The problem is it won't turn off. Air direction is not a problem as he can direct the heat to any location. Adjusting the temp setting does not change the temp. I removed the knob and verified that the switch was turning. Since I have heat I assume (maybe incorrectly) that it's not a clogged heater core.

There is also a clicking noise coming from the area of the glovebox/airbag. I don't know if it's connected to the heat issue, but wanted it to put it in the post.

Thanks in advance! It's 75 degrees here and with the heat on high I need your help.

Automatic or manual controls.
If automatic remove glove box on see if the clicking is coming from the actuator motor on top of ac/heater box.
Up in the how to there is some pictures and info on it.
MT

This link here in how to section.
http://www.automotiveforums.com/vbulletin/showthread.php?t=574779