More or less behind the center console. Not real easy to get at, and there is some kind of power module I've seen referenced that may be more suspect. Search messages for ECC or electronic climate control or similar. There are a few threads on similar problems, but most deal with problems in the auto mode...mine happens in manual mode, so I don't know if the ECC module is a problem or something else. Heat and air seem to work ok. Also clean out the temp sensor as some of these threads point out.