I dont have the manual but i will try doing the steps you said tommorrow and see what codes there are. I am going to try and disconnect the control valve and just bypass it see if that works then i know its that the valve is stuck. I fnot do you know how to unclog the heater core and where is the blend door located, when i push the buttons to control the air flow from vent,floor or defrost i here it working. To answer your question it wasnt to hard to get to the tstat you need a shallow 12 mm socket with a short exstention and need to loosen the alternator adjustment bolt so you can get the serpintine belt loose to reach the bolt on the tstat.
I tried doing the diag on the climate control and it did nothing i hel the auto sitch and the front and rear defrost switches and turned the key to on and nothing happened.I am going to try and bypass the control valve by the firewall and see what happens