99 galant no heat

I tried to install a new thermostat but when I removed the housing there was nothing in it and the t/stat would not fit is there a second housing behind the sensor that I didn't find?

I just had this same problem with my 2000 galant where is the thermostat located on the 2000 galant 2.4 i also took housing off and there is nothing there and thermostat wont fit in the housing!!