Said it before, I'll say it again.... the "manual" system isn't manual. You select the fan speed and the air direction, but the system still controls temp. There are still vacuum pods moving the air doors. In addition it's dual zone. I imagine everything is different from the heater core, water valve, control units, air dampers.... if you're looking to save money it would be cheaper to get the fully automatic system working again since parts abound.

The automatic system really isn't all that complicated... a few temp sensors, the pushbutton unit, the control unit, water valve, the vacuum valves, and the blower.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.