Why don't I get Hot air out of the Vents? on 2004 Chrysler Concorde

I can turn the temp dial all the way to hot and the air is still cold. The return heater hose seems cooler than the other @ the firewall. How can I test the temp dial switch or the valve that controls coolant flow through the heater core.

Asked by for the 2004 Chrysler Concorde
I would start by checking the blend door operation