Always steaming heat!

I own a 1999 Blazer V6, automatic transmission, Auto 4WD and Computer Climate control. No matter what I set the temp-knob at, it is always at full blazing heat! Fan control works, it goes from zero to full storm reg. to setting. Air vents works as well, air is coming out where it´s supposed to reg. to settings. AC works as well, when checked, the linings turns ice cold when running. I´ve read somewhere that the main heater door could get stuck in its outer posissions, either at full heat or at full cold. Could this be what´s happend? Is there an easy way to check this? I´ve been thinking about taking the wires off the main heater door motor and measure the voltage as turning the temp. knob - is that a possible way? or can one reset the damn thing? or is it a computer issue - and what to do in that case? My son is under car mechanic education - do you think it is possible that this would be a case for him and his mates to fix? Please help as this is driving me crazy! I don´t want to leave the car with my local Chevy dealer, as we live in Sweden that would cost a fortune and I don´t trust them either!
Any help in this matter is greatly appreciated! If any one has pictures or any other info that would be great as well!
I know you guys have worked out solutions to all sorts of problem and I trust someone of you have had similar problems on your cars as well.
Why is the Blazer prone to be a such a problem car?! All american cars older than 1975 I have known before never, never had problems like this one!
I have to tell you that once this problem is fixed I will swap it in for a SAAB 9-5 or Volvo V70 as soon as possible, and probably have a fifties or early sixties Chevy or an other GM car for fun! Never ever that I will buy a newer american car again as this is the most expensive problematic car I have ever own!
Thanks in advance guys -I love this forum!
 
 

ok first off, dont trade it in for a volvo they suck , plus they cant go uphills very well. lol
 
second, i would try swapping out the switch/s whatever controls the settings for the heater/ac .. try a junkyard as you would be able to get pretty cheap and will work just as good as new (least ive been pretty good at finding good stuff at local junk yards )

The first thing I would do is make sure that the interior temp sensor is functioning properly.  Sometimes they get clogged with dust and do not read properly.  On my old '00 Bravada, this was located kind of above the driver's door and looks like a very small speaker grill. 

But this does sound more like a air temp actuator problem which is an electronic actuator that is located on the far right top side of the HVAC housing and requires the removal of the dash carrier (the whole dash) to replace.  Before going through all of that trouble, I would remove the RADIO BATT fuse for 30 seconds with the ignition OFF and then reinstall and turn the ignition to RUN and wait until the HVAC system goes through its checks (could take up to 2 minutes).  If that helps, good deal, if not, atleast it only took ~5 minutes...

Thanks guys!
I can hear the temp sensor working with ignition on and engine off. Does it have a small fan of its own? Which is the easiest way to get it out for control? I´ve tried to get it out but stopped as it seemed like I would break it or things near to it....
I will try the radiobatt fuse metod tomorrow!

Nope, the Radio Batt fuse method didn´t work - but I noticed yesterday, when the engine was hot after driving it, that when both the fan and direction knob is set to Auto and temp is set at full cold, hot air is coming out through the far left, far right and the two outlets in the middle. When temp is set to full hot, hot air is shifted down to the two outlets directed to the foot wells??....
Otherwise things are as before.
Swartlkk, how does one clean the temp sensor above drivers door (I heard it humm after I did the fuse test) and do you have any other suggestions? Would a code scan help?

As far as the temp sensor is concerned, you can blow it out with compressed air.

I don't believe that the s-series trucks have a duct temp sensor, but I'll look into that if I get some time today.

Thanks Kyle!
I will clean the sensor and see what happens! Is it normal that one can hear it working?
This problem occured after jumpstarting the car several months ago - I don´t know if this will help you in any way, just thought that I´ll mention it...
What happened was that when we tried to get the car started every lamp and warning light in the dash flashed a couple of times then went back to normal when the car started, and since then I have this problem. I changed both battery and alternator shortly after the jump start.