I'm betting the hose that goes to the L side windshield vent is disconnected or missing. It typically happens on the driver's side because that's where people are typically in the dash doing something like instrument cluster or ignition work. There is no control to separate the L from the R side windshield vents.
Best Regards,
David
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2000 Honda Accord V6 137k miles
1972 300SEL 4.5 98k miles
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