Cadillac Repair: 1990 climate control, buick park ave, climate control system

Question

Climate control panel I have a 1991 Buick Park Ave that uses the same climate control system as Cadillacs of that era.  When I try to put the system in "AUTO" it automatically reverts to "ECON".  All of the other options work.  The Auto Button beeps when pressed but the Econ light comes on.

Answer
The reason that the ECON light is coming ON is that you have a problem in your AC system which could be just low on FREON (refrigerant) due to a leak or a sensor problem.

Without you putting a set of AC gages on the AC system and seeing what the running pressures ARE. There is no way that I can determine if you are low on freon or you have a faulty sensor.

What are your HIGH & LOW side pressures with the engine running ?.

Without knowing what the pressures ARE, The problem could be any number of sensors, modules, relays, controllers, etc, etc.