Does your temperature door make noticeable movement sounds when you go from hot to cold to hot? with air blowing? try pinching off heater hose and see if that lets you know if temp door is in correct position...
'95 Chevy 3500 454 Dually 142,000 miles
'94 Chevy Astro Van 358,000 miles!
'86 Buick Park Ave 192,000 miles
'86 GMC S-15 Pick-up 150,000 miles
'92 Chevy Lumina Van - 265,000 miles- given to me to see how far it can go! all above are white!