Heat problem?

Now that I fixed my A/C, here's the next problem:

'92 Lumina 3.1L

I have next to no heat in my car and I'm not sure why. I can put on any temp selection (A/C, Vent, Heat, Defrost) but it only comes out on the "cold" setting. Blower motor is fine and for this case, we'll assume i just have it on max.

When the temperature control is moved all the way to the left to "cold" the air will come out full blast. However when i move the slider to "hot", it seems like the air is only coming out 1/4 the speed it was on "cold". The air itself blows cool when it's on "hot". Of course it feels hot in the summer time, but in the cold months...it's cool.

Any body have any ideas? Are there seperate intakes for the "cold" and "hot" settings? I'd like to fix it now before it gets really cold.

I took apart the whole underside of the dash again because i thought maybe there was gunk on the back of the heater core which was interrupting the flow. No luck, the core was just fine, so now i don't know where to go from here. Maybe a flapper door/ vacuum problem?

I wish there was some detailed diagram that shows the FLOW of air through the Lumina's system so i could figure out what the problem is. Right now it's process of elimination and what i thought it was, wasn't! :banghead:

Any help anybody can provide is greatly appreciated!

Well, I have heat again! I gave in and took it to a repair shop. Had them replace the heater core and sure enough, that was the problem. I had them show me the old core and sure enough, there was stuff between the fins. Looked like mold mixed with dust. There was nothing on the back of the core though, which is why i thought it was fine. I'm guessing it was from when my A/C was plugged and I kept getting water in my interior. Guess it clogged that up too. I'm happy things are back to normal and I'm warm. :p