Are you stating that the aux. fans are not operating when the A/C is on?

If so, have you checked the aux. fan switch at the A/C receiver/dryer? There are 2 switches on the dryer, one for the freon pressure to shut off the compressor if the high pressure gets too high, and one for the aux. fans (this is the one with the pigtail). This one could be the one that is not turning on the aux. fan when the A/C is on.

Keep in mind that the aux. fan serves 2 purposes...
1. to cool the radiator when needed.
2. to cool the A/C condensor.

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible