Toyota Repair: Fans on the radiator, temperature sensor, thermostat

Question
Hi Ted,

I have 1993 4 cylinders camry with A/C and Automatic Transmission.
I changed its radiator because it started leaking at the top.
I have two questions for you.

1) None of the fans comes on when idling  at parked position.
Both fans start working when I turn the A/C switch and the car is still in parked position.
The car gets a  very very small drip at the bottom of the radiator where the temperature sensor is screwed in. I am sure I did not cross thread when I installed that. Am I suppose to put some putty on the sensor's threads before installing it? I did not put any things on the threads at time of installing.

Please give me your expert advice.

Thanks

Vijay

Answer
There is no reason to put sealer on the threads of the sensor.  If the engine is not getting to the correct operating temperature the fan will not come on, this may be due to a stuck open thermostat or a missing thermostat, try replacing the thermostat first and see if it will help.