Hey Steve. This is taking me back aways, but I seem to remember these buttons getting stuck by food and dried beverage syrups (sweetened coffee, Coke) getting in between and behind them. So remove the panel and give it a good cleaning and drying to start.
I had the same problem and for me it was easy fix there is a vacuum line that runs into then out of a vacuum canister then through firewall which changes the settings. It is top of firewall in the open by air intake for blower motor and towards engine from windshield wipers
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