When the heater only works on high, the most common problem is a blower motor resistor. The correct repair is to replace it with a new resistor.Google+
Car Problem Reports
Buick Century Heater only works on high
Buick Century Problem
Average Mileage: 117,333 mi (73,000 mi - 200,000 mi)
Visitor, 2002 Buick Century, 116,000 mi
My heater AC motor does not work on the lowest two settings.
My heater only worked on high before, and when I would turn it on it would make a horrible screeching sound. The thermostat turned out to be bad, once this was replaced, it seems to work a lot better.
Visitor, 1999 Buick Century, 73,000 mi
low does not work
Visitor, 1999 Buick Century, 200,000 mi
No heat unless I turn it to high
Visitor, 1999 Buick Century, 84,000 mi
heater only works on high
my heater only works on the high setting, when i turn it on high it makes a loud noise and does not blow heat.