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Sounds like a bad switch to me. Kind of like when you have one of those lights in your house that will get brighter with each turn of the switch but at some point only one stage works.

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Check the blower motor resistor bank.

I don't know your specific truck, but the blower motors typically work by putting a resistor bank in series with the motor. So for high speed, the full 12 volts is given to the blower motor, and it works full speed. Lower dial positions, put larger and larger resistors in series with the motor, which drop the voltage that the blower motor receives, and it runs slower.

This is typically mounted in the HVAC plenum, so that the moving air actually cools the resistors (since they get hot dropping the voltage). Look under the dash, look for some wires connecting to the side of a plenum position, which has something that can get unbolted from the plenum. Visualize a small panel, bolted on to the side of the plenum so that it can be taken off, and then that panel has a connector and some wires to it.

Take that out and check out the resistors, I think you'll find something burnt or a wire broken.

Good luck

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Just realized, this is a 2006 vehicle. This is covered under warranty (assuming mileage is ok). Take it to the dealer and let them worry about fixing this.

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This sounds like the resistors are blown in the circuit. There is a resistor bank/group as mentioned above, the resistors are wired one per speed and it sounds like the lower bank is blown and just the high is still intact.
The resistors(in this setup) are basically wires that heat up and cool down causing the resistance and after doing this many times they have a tendency to break from all the flexing involved when heated up and cooled down.

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on a dodge stratus auto their is a small plugin flat loooking /sensor under the dash passenger side that I replaced My car was doing same as you described
It solved my problem.

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Late model Dodge trucks have been known to have this problem. Your blower resistor took a crap. It is located in you heater/AC case under the dash.

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