Question on Rear Blower Motor Fan Switch?

Hello:

I have a 2002 Chevy Suburban with 130k miles. I have a problem with the rear blower fan switch (both ceiling controls - front and rear). The problem is as follows:

When I turn on the rear blower fan to SPEED #1, there is no low speed air at all. When I turn the fan up to SPEED #2 or SPEED #3, it blows at MEDIUM speed. Finally, when I turn the fan up to SPEED #3, it blows normal on HIGH.

Side note: The blower fan switch for the driver's compartment (located on the dashboard) is working properly.

I was told that it may be a rear blower resistor, but I am unsure if my Suburban even has a rear blower resistor. I know for a fact that it has a front blower resistor (located under the passenger side of the dashboard). I was also told that it could possibly be a blower relay?

Please steer me in the right direction on this problem so that I don't spend on parts that I do not need?

Thank you very much in advance.

Jim in AZ