Well, I got a call from my wife on her way home from work today.
'what do I do when the windows get all fogged up?
You turn on the heater.
'I have it on and tried all the settings, hot, cold, fresh air, recirculate, AC. nothing helps. I have the windows open but am getting cold.'
Just wipe the windows with your coat and I'll check when you get home.

As soon as she opened the door I could smell it. The dreaded coolant smell, coming through the vents. Next check on Blazer forum for help. Search 'fogged windows coolant smell'. Two results and both deal with the heater core. I went out again and checked under the carpet; dry and no smell, checked under the hood; radiator full, overflow empty. All hoses and clamps look OK.
I guess I gotta bite the bullet and change the heater core now. I should say that I had the cooling system flushed in the summer, from what I found on here that is a common catalyst. So don't ever flush the cooling system would be my advice. Now I am going to check my service manual and see how big of a job it will be. (Blazer forum before GM service manual, you all should be proud.)

I have AC and auto heat, It seems like this means alot more work to get to, remove the heater/vent module. Remove right wheelhouse panel, tire, raise vehicle, lower vehicle. Or am I just reading more into it?

 

Yep, sounds like you'll be tearing the dash out. You could try some of the GM sealer tablets, but they are more of a bandaid on a 6" gash than anything else. May get you by for a bit though.

And the "don't ever flush the cooling system" comment is primarily how your core got in a bad way to start. Routine cooling system maintenance is a requirement. If left unmaintained, bad things can and will happen.

 

Yeah, you are probably right about that. I was/am amazed at the lack of maintenance on my blazer. Over here american cars are a big thing, alot of people have them and there are several AM car clubbs around. Anyway I bought the blazer from a guy that has an immaculate 73 mustang, (he used to work as a detailer), is a member of a local club that houses some of the nicest/cleanest old cars around. But my Blazer on the other hand hardly got any maintenance. I found rotten plug wires, old worn down plugs, very old oil filter (stuck on), a 6 year old fuel filter. I couldn't believe the difference in how he treated the blazer and how he treated the 'stang. If you are an entusiast, you are an entusiast. I hated my last car (suzuki baleno(esteem) stationwagon) but I still maintained it.

Back to the problem at hand, is there anything else I should replace/service/check while I have the dash apart?

 

mmmmm smells like waffles! I'm in the same boat as you, see also my thread in this forum titled something like 'Man up or Pay up' as my mechanic quoted me 550 bucks for 8 hours of labor to do mine.

 

I know how it feels, when I returned home from a deployment I did a routine check on my 2001 blazer, found that my oil was saturated with coolant, had a crack in the radiator tank(2nd time). After replacing the intake gasket, oil change, and switching out the dexcool, my heater stopped working. First thought it was a bubble and let it run with the cap off for a good while, refilled and bam, it worked for two days. Changed out the thermo and it worked again for a day or so. So I guess I get to change out the heater core and will get the door acuator at the same time. Not to excited. Blazer has been noting but problems since I got. Blown oil line and cracked radiator tank two days after getting it used, has codes P0440 and 410. And to top it off yesterday on my way to work I switched lanes to avoid hitting a minivan that was sliding on ice, I ended up sliding myself into a deep narrow ditch at 55 mile an hour. Destroyed the left side bumber, and corner panel and broke the passenger side axle assembly. I have put more money time and money into this thing that its worth, and Im still keeping it, maybe Im crazy or just stupid