[s-cars] '92 S4 - AC won't stay on

[Airbil]

Just a guess,.... But based on my experience from last year, spring could be a good to great time to check:
The fan clutch.
The auxiliary fan.
If you've never changed your fan clutch, do it.
The aux fan will freeze  / corrode up and blow the 25/30amp mother of all fuses in the driver side footwell.   Sfest is a good time to fix this.
But I digress.
I "think" the recirc may look to the aux fan and if it's not running will turn off the ac then.
My .002.
Aircooled ~Bill m
                         ~ via airbil's cosmic transmitter ~