Cooling Trouble shooting

Hypothetical: Not my Jeep... but If my aux fan is not coming on at any time except when the A/C is on, even when the temperature is over 230 (IR gun). When A/C is on the aux fan works fine.

If I unplug the coolant sensor and the fan comes on (over temp, not with A/C on) does that mean my sensor is to blame. Relays check out fine.

ParadiseXJ said:

If I unplug the coolant sensor and the fan comes on (over temp, not with A/C on) does that mean my sensor is to blame.

Click to expand...

That would be a logical assumption.

ParadiseXJ said:

Hypothetical: Not my Jeep... but If my aux fan is not coming on at any time except when the A/C is on, even when the temperature is over 230 (IR gun). When A/C is on the aux fan works fine.

If I unplug the coolant sensor and the fan comes on (over temp, not with A/C on) does that mean my sensor is to blame. Relays check out fine.

Click to expand...

What year is it? That makes a difference, which coolant sensor location?

Well, As I said in my OP it's not my Jeep...it's not a Jeep at all. It's my 02 Nissan Sentra. I know this is an XJ site but all the Nissan sites are slow in coming with any info. I know that I can usually get an educated response around here within an hour or so.

My coolingfans (both electric) were not working at any temp, except with the A/C on, and even when it cycled off the fans would go off. The thing was running fine, but when the A/C cycled off it would start getting hot. Once it got over 200F the fans stayed off and it KEPT increasing the heat. Then it would overheat and boil into the overflow. I was considering (dreading) a head gasket, but there is no crap in the oil or coolant. Compression fine in all 4.

Long story short, I replaced the sensor/switchand all is well now. Thanks for looking.