Blower motor fan speeds not working correctly?

You can use a testlite on the wires for the blower speeds. In the diagram you have one wiring color for each speed, take the connector loose from resistor assembly. key on, havc turned on, switch through the speeds, while you use a testlite at the proper wiring color at connector. If everything is hot, probably ok up to that point.

The resistor assembly is under passenger side of dash, number 5 in the picture.

For you to have 4 and 5, but not the other 3 would have to be the switch in the dash, or the resistor pack. This guide can show you how to check the resistor pack

https://www.2carpros.com/articles/blower-fan-motor-works-on-high-speed-only

Please run down this guide and report back.

NAPA is showing it to be about 25 bucks

Hello,

It is most likely your Blower Motor Resistor it is located near the blower motor under right side of dash and it looks like this.....

Hello and thanks for the donation!

There is a common issue with this year's HVAC fan only working on the Low & Medium speeds. There should be a 2 or 3 wire cannon plug in-line between the blower relay and the 50-Amp fused circuit from the underhood fuse / relay box. This plug and another share a niche rolled up in adhesive foam in the vicinity (top of airbox, right of the relay) . This plug commonly burns up and fails.

(SNAPSHOT OF FAILED PLUG)

You'll need to replace the resistor.

It'll be near the blower motor. On GM vehicles it'll be on the passengers side under the dash.