difference between top coolant sensor and the bottom sensor on radiator.

First, the fans may turn on regardless due to the air conditioning system being active. If this is the case, the condenser fan will run regardless off engine temperature. The compressor may run even if air conditioning cooling is not selected -- it also operates with multiple climate control settings regardless of temperature desired. Regarding connections - why is it disconnected? That sensor is the engine coolant temperature sensor and is important. Check and fix this - is the sensor working? https://repairpal.com/auto-repair-near-me Click the link or call us at 877-913-1554. We'll gladly find you a certified RepairPal shop in your area.