I don't know about your 1990 model, but my 96 will only turn on the fans if the outside temp is 86 degrees or higher, unless of course the engine temp or Freon pressure gets up there, which it usually doesn't unless it is hot outside. This was a learning experience for me as well because I thought something was wrong with the car as I would figure anytime the AC was on the aux fans should come on, but I guess with the lower temp and the engine fan, it is enough to keep the AC cool. I did replace my fan clutch because while in traffic the engine temp would get kind of high and I don't want my little motor to get too hot! ha ha.. Good luck!
Brian

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Brian W. Heitman

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