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.

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2 answers
blower motor resistor block should be by or on motor
Cogcan is right and here's what it looks like https://partimages.genpt.com/largeimages/482402.jpg around $27 at Napa