I have a 99 deville 4.6,when I run the ac the fans run fine and you can drive on 1999 Cadillac DeVille

but when you shut the ac off the fans quite and do not come back on period. I replaced the fan relays and the ect sensor. Something should tell the relays to turn the fans on when the engine gets warm but it's not. What sensor does this. Can you help?

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