This could be either a broken knob or a broken control valve. Pull both knobs off and compare the stubs sticking out of the control panel.

Actually, try the right knob on the left control and see what you get.

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Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References