What needs to be replaced on a 2000 Oldsmobile Alero GLS if the air conditioner only works levels 3 and 4 not 1 2?

The fact that your 2000 Oldsmobile Alero GLS AC only works on high speeds (levels 3 and 4) suggests a problem with the blower motor resistor. This resistor controls the different speeds of the blower fan. When it fails, higher speeds might still work because they bypass part of the resistor, while lower speeds are cut off due to the resistor's failure.

Therefore, the most likely component needing replacement is the blower motor resistor.

However, while highly probable, it's not guaranteed. Other possibilities, though less likely given the symptoms, include:

* Blower motor itself: A failing blower motor could have trouble reaching lower speeds. This is less likely than the resistor as the motor usually fails completely rather than just specific speeds.

* Wiring issues: A short or break in the wiring to the blower motor or resistor could also be responsible. This would require more detailed electrical testing.

* Control panel issues: Though less common, a problem within the climate control panel itself could also be preventing lower speeds from engaging.

Recommendation: Start by replacing the blower motor resistor. It's the most common cause and the cheapest/easiest fix. If replacing the resistor doesn't solve the problem, then further diagnosis (likely involving a multimeter) will be needed to check the wiring and the blower motor itself.