Your freon level is too low. Have it topped up and dye added to check it later for leaks. I had a very similar problem with a 2000 Olds Intrigue.
Bad "blend door" actuator or stuck blend door on the driver's side.
because someone was fiddling with the passenger climate control and now that baffle has stuck in the cold position . I had a 1997 buick lesabre which had the climate control functioning until a friend started adjusting it a few times then it became stuck in the cold position but only for the passenger side It is likely a mechanical bind in the baffle .
When my a/c system is low on refrigerant, it blows hot on drivers side, cold on passenger side of the dashboard. This is a 1997 Buick Ultra. Recharging the system solves the problem.
usually system is low of freon when this concern occurs. if 134 freon is ok then temp doors may be out of calibration. djones1
If the 1990 Buick Century transmission is only shifting well when it is cold, you have to rebuild this transmission. It is likely that the clutch packs or clutches in the transmission are damaged or worn.?æ
Temp blend door actuator malfunction.
Try to replace the oil filter if the transmission is not engaging when it's cold.
Check to see if you have a dual climate control. There are usually two sliding levers on top of one another. Slide them both to cold
You may have a loose vacuum hose either under your dash, or in the engine compartment.
Has a bad blend doot actuator. It is under the dash near the ducts, and it looks very hard to change.
the problem is a part called the air temperature control blend door actuator motor, it is deep inside the dash and the dash must be removed to replace it.
Make sure your radiator is full of coolant