I have a 93' Seville, it has always had amazing heat within a mile or 2, now the blower comes on ( as always ) but it blows really COLD air.
I have checked the Thermostat, hoses, heater core, and Bypass control valve, and fluid levels, the hoses are HOT but air is cold.
I have also watched the "programmer" open and close the gate from a/c to Heater core, so that is working.
I suspect air routing baffles ( maybe a " RE-CIRC " ) or doors may be the problem because in the engine bay I can feel a strong source of cold air being blown out of the a/c coil enclosure ( engine bay side).

Any thoughts on this ? Does anyone know where to to find schematics for the heating system or actuators ?
( GM has nothing ? and no clue) I have a a (8420)28540 CHILTON"S manual but it does not cover any of this nor does it have any wiring schematics,

You need a factory service manual for detailed information. You can get one new from Helm, Inc. (http://www.helminc.com/helm/homepage.asp?r=) or try Ebay.

Another possibility is that the heater core may have become clogged. Has the coolant been replaced on a regular basis? You might want to disconnect the two hoses to the core and flush it, then replace the coolant with the pellets.

Kev is correct. Chiltons is useless for all but the most basic of repairs. Get a FSM from Helm Inc., but flush the core first.

As I had said , I have removed , inspected, flushed and reinstalled the heater core, and cleaned the A/C coil filter while I was there. I also went the other way and removed the ECC power module from the engine bay side to inspect that side of the A/C coil... Clean

Sorry, but I fail to see where you said you flushed the heater core.

Sorry , I thought I had covered that, Yes, I had checked the Heater core, first by back washing, then by taking the entire unit out and inspecting it in the sink. Clean as whistle.
after the previous inspections, I've mentioned...
I decided that if the bypass was stopping all the fluid from reaching the core, how about chocking off the bypass( I used a padded hose clamp around the bypass line)... worked like a charm,... so I thought , if a little is good, a lot must be better... right about then the bypass control valve ( tee ) blew apart and I got soaked with hot anti-freeze... okay , so after hands and face in the snow,
I put on a new bypass control valve "tee" , topped up the system, and let it get hot, I felt air bubbles in the lines, so, after it cooled down I re-topped it up and it now works great... almost instant hot air
Not really sure why but it's working ... so :)