Fan Controller problem GM vehicle

[xplcitcustmz 10+ year member]

Anyone else ever have a problem with this. I turn the heater, or the A/C on, and it only blows high, their is no other choices, high or off. when i put it on low or medium, it just blows high. Could this be a problem with a resistor or something??, best way to fix the problem? should i replace all of the heating controls??.

By the way this is for a 99 suburban base model

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