Cadillac Repair: 1999 STS AC intermitant cooling, center vents, freon

Question
QUESTION: Is there a way to reset auto cooling in 1999 STS, eg,disconnect battery, etc. Pressures good.Cools awhile, then blows warmer,but still cools.Have gone to full hot and back to cold.Blows only cool air but not cold.. Thanks

ANSWER: Has any work been done to the AC/Heating system ?.

Is this warm air being expelled from ALL the center vents ?.

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

QUESTION: No..
Yes..

Answer
What are your pressures ?.

IS or HAS the CHECK ENGINE light on the dash ever illuminated while driving the vehicle ?.

Have you seen any messages in the message center such as LOW REFRIGERANT (freon) ?.


Problem could be:

Low refrigerant.
orifice tube restriction.
damper door not closing all the way.