The most common issue is the heater / climate control valve. This can usually be tested in dual mode and checking for change in air circulation.
Where is the heater control valve on a 1994 Buick Regal
were heater control valve for 1996 buick park avenue
How to fix heater in Buick there is cool air ,fan is work .but no warm air
Thermostat stuck open or heater core clogged. Bad radiator cap or small hole in cooling system.
possibly when the a/c is not needed to cool the air temperature you set. The A/C control module has failed, as revealed on a diagnostics check.
take one end of your heater hose off the heater core and run it back to the intake port.
There is a fellow on Ebay that repairs these controls. It is easy to remove from the car and he will repair your control and ship it back out in 24 hours. He repaired mine 15 months ago and it still works perfectly. His eBay username is "musclos1" The title on his current ad is "1998- 2000 Buick Regal Century Climate, Heater Control" His current price is 36.95 including shipping.
If the sensor is blocked or has mud on it, the readings will be inaccurate, and give completely false readings.
may be your heater control valve
Low freon
My 1999 buick regal temperature control LED readout is stuck on 32 degrees for high and minus 2 for low. It still works but is there a way to reset LED reading? Thanks in advance
How do I replace heater core on 98 Buick lesabre