fans coming on with coolant sensor unplugged

[steve1ph]

i have another question. why would both fans come on at start up when the coolant temp sensor is unplugged. when they wont come on when either i cross the switch over or have it plugged in normally? trying to change the a/c over but trying to get the fans working right. iv had an external switch hooked up but getting tired of messing with that. replaced both fan motors, relays ect during recent engine rebuild, were working, now they are not. maybe the sensor? the car is a `90 model 6speed.

 

[handstjg]

Your temp sensor provides the ground (negative) side to your fan relay coil. Check to see if temp sensor wire is grounded between the sensor and the relay.