As mentioned, I picked up a 1991 Honda Civic base (198k mi), and I noticed this on/off toggle switch wired in where the 12V outlet used to be:



When the engine is running and you flip the switch to on, the a/c goes full blast, and toggling the control *** above to any of the 4 power settings does nothing at all (including the OFF position, only the toggle switch can shut everything off). This was installed several owners prior, and the most previous owner to me has no idea of the purpose either. Currently, no cold air is blowing out, but I'm hoping that can be resolved with a recharge using r12a.
Thanks for any help you can give me!

 

They have apparently bypassed the power resistor that controls the fan settings. Should be an easy fix. Check your blower motor for the resistor.

 

The resister probably went bad, so they just toggled the fan to an on and off switch. Check the red wire on the compressor first. It may be missing or not hooked up.

 

heater resistor information

https://honda-tech.com/honda-crx-ef-.../#post43614305