My wife just bought a 2001 Deville but the interior temp flucuates, it warms up to almost to warm then cools way down to where she says its to cold. She can turn it up and down but thats a pain. Her Olds never had this problem.
After searching this forum I see some problems with the heater cores sludgeing up.
Or is this a dealer type thing where they can test the functions of the auto unit.

you may want to check the inside air temp sensor, may not be reading the correct temp.

you may want to check the inside air temp sensor, may not be reading the correct temp.
Sounds like the right thing to do,