My heater just recently started blowing only cold air on every setting. I took the glove box out to look at the control linkages and sure enough the temp adjuster linkage was off so I hooked it back up and it still wouldn't blow hot air. So now I took the hoses off of the heater core thinking that it might be clogged. I took an air nozzle and stuck it up the heater core inlet and blew some air through there and it seemed to flow freely. Next I stuck a water hose in there and the water seemed to flow through freely as well. I figured that wasnt the problem so I took the front piece of off the air box under the dash to look at the doors internally and all of them seem to be functioning properly with all of the vacuum hooked up correctly and working. Where should I look next ? Sorry that was a long one but there are a lot of details. Thanks!