This is direct from the 1997 Service Manual
Automatic Control Air Conditioning page 1C-15
DISPLAYING DIAGNOSTIC TROUBLE CODES
The only way to display diagnostic trouble codes (DTC'*) is by using a scan tool. There are no provisions for "ON-BOARD" diagnostics.
If you are referring to the switch, I have it installed now and any time the ignition is on I have the choice of manual Low speed, manual High speed, or computer controlled.
If you go that route PM me. I have some suggested changes in the directions they send.