Cadillac Repair: 1993 cadillac deville, jim fitzpatrick, heat situation

Question
first off, i'd like to say that i make my living as an automotive technician, so feel free to be technical.i've got a 1993 Cadillac deville with the 4.9 and i have a few problems and i wonder if you think that they are related, first off the car has an intermittent hard start after about a 15 minute cold soak, the heat doesn't work, i have replaced/flushed  the heater core about 5 times, when i do the car has heat for about 2 weeks. and then it goes back to blowing cold air, i tried disconnecting the a/c compressor thinking maybe it was stuck on. that made not difference. i have checked the blend door and it seems to be fine. . i have heard that oxidation from the aluminum block breaks off and clogs the heater core and if that is the case, what can i do as a permanent fix? i thought maybe some kind of a filter in the inlet hose of the heater core??? also, i cannot get the heat to blow out the vents. only floor or defrost. i have had the car to the Cadillac dealer and... they are baffled
what do you think?

Jim FitzPatrick

Answer
Intermittent hard start can be caused by no or weak spark to the spark plugs which you will have to check the spark efficiency to the plugs when you know the hard start is going to happen.

Next would be a weak fuel pump when the pump is hot. check the fuel pressure/volume when hot.

intermittent fault in the AC/Heater PROGRAMMER located behind the glove box liner. Remove the glove box liner and watch the threaded metal rod for proper operation. When the plastic arm that is connected to the programmer arm via a plastic snap connector is fully towards the passenger you have full heat and if arm is away from passenger and towards firewall this is the full cold position. Watch the rod for non movement when you have the no heat situation.