Heater blower on 1990 Pontiac Bonneville

Heater blower only works on high.
All other settings blower does not work.
What are things I can check on.

Asked by for the 1990 Pontiac Bonneville
Cogcan is right and here's what it looks like around $27 at Napa
1 more answer
blower motor resistor block should be by or on motor