Cadillac Repair: no heat drivers side, cadillac sts, center vents

Question
QUESTION: I have a 1992 cadillac sts 4.9.blower and heat control seem to work fine for the passenger side but the drivers side lacks any type of real heat and not very much air is being moved by the blower.I get a little heat on the floor but nothing for the front defrost drivers side.can u tell me more about these vacumms lines  I have been told about and where do u find these. thanks very much for the help first time I have been here, hope to be back.

ANSWER: If you put the system on defrost, Do you get hot air from both dash vents ?.

If you put the system on , Do you get heat from both sides of the passengers compartment ?.

If you put the system on A/C do you get cold air from ALL the center vents as well as the drivers and passengers vent ?.

Has any work of anykind been performed on the vehicle prior to this problem ?.

---------- FOLLOW-UP ----------

QUESTION: Hello there,with the system on defrost you only get heat from the passenger side dash vents.the passenger floor vents work fine also, all kinds of heat all the way across the floor,but no heat and no air from the drivers side dash vents and very little heat and air on the floor of the drivers side.As far as the a/c goes I was told from the guy that I bought it from that he unplugged the compressor because of a leak he had.I use to get a code saying a/c compressor turned off but it no longer comes on and my economy,auto, and defrost functions seem to work fine,just lacking  heat real bad on the drivers side.The center dash vents don't seem to work at all,It does not matter what setting you have it set for,there is no air at all blowing out of the center dash vents.Can you tell me why? I was told that air is suppose to blow in thru the centers vents all the time but I don't get any at all.Thanks for the help.

Answer
The ONLY time the center vents emit air is when the A/C is operational.

Your problem is most likely with the up-down actuator valve which is not diverting the air to the floor vents.

You will need several pictures and specific directives showing you how to test theis up-down valve.

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