2002 Liberty electric rad fan is always on when running

[Bigmoe]

So My daughter was out with her Liberty puttering slowly in the countryside and stopping to take pictures of birds (she's got a cool 85x zoom) when the Liberty overheated. Of course she called Dad. By the time I got there it had cooled off some. After some investigation I noticed the fan blades were off the electric motor. It stayed on normal temp driving home with some speed and wind blowing over the rad. I initially tried rigging the blades back onto the motor but the assembly is worn and wobbles so I ordered a new aftermarket assembly (motor and blades).
Another problem though. When it's running the fan is on all the time even from a cold start. I assume it's supposed to come on when the temp climbs high enough? What might be wrong?

 

[uss2defiant]

Here's the turn on/off conditions for the e-rad fan.
It could be a number of things.
With these early KJ models, the fan speed is modulated via PWM to a solid state relay from the PCM. There is a SB to replace the smaller factory SSR to an updated version. This relay should be bolted some where on the driver side where the wheel well is.

One of the things that I noticed too from my issues is the e-rad electrical connector had melted due to high resistance(corrosion or bad contact) and I had switched it out to a better connector but this doesn't sound like it relates to your situation but I'd check on the connector since you are 'servicing' it. Look at the open end of the connector into it and inspect for any signs of melted plastic.


OPERATION
The electric radiator cooling fan is controlled by the Powertrain Control Module (PCM) through the radiator cooling fan relay. The PCM regulates fan operation based on input from the engine coolant temperature sensor, battery temperature sensor,air
conditioning select switch and vehicle speed. The fan is not energized during engine cranking regardless of the electrical input from the temperature sensors and ,air conditioning switch. However, if engine operation conditions warrant fan engagement, the fan will run once engine starts.

Vehicles Equipped with AC:
In addition to using coolant temperature and battery temperature sensor to control cooling fan operation, the cooling fan will also be engaged when the ,air conditioning system is activated. The relay is also energized when, air conditioning is selected and coolant temperature is above 95° C ( 203° F), or , air conditioning is selected and battery temperature sensor is above 41° C (106°F). It will then de-energize when , air conditioning is selected and coolant temperature is below 92° C (198° F), or , air conditioning is selected and battery temperature is below 38° C (100° F).

 

[Bigmoe]

Well it's too cold here for it to come on upon starting. I made sure the A/C wasn't on. I wonder if that solid state fan relay is the culprit?

 

[uss2defiant]

could be a bad battery temp sensor as well.

 

[Billwill]

Good advice here from uss2defiant!

The 2002 KJ Service Manual section 7 gives an explanation of how the cooling system works and states that if too many errors are found with the Fan Relay then a DTC could be posted.

Section 8W has the wiring diagrams that show the Fan and the solid state relay but only for the Diesel model...such as I have! No wiring diagram for the Gas models but this it is not unusual for errors to show up in these wiring diagrams!

The Battery Temp Sensor sits under the battery and is supposed to affect the turning ON of the fan and also has an effect on the Charging System....changing the rate that the alternator charges the battery according to the temperature that the Battery Temp Sensor is sending out.

This Battery Temp Sensor is a Temperature Variable Resistor. On my 2002 Export CRD years ago I suddenly got the red Battery light come ON...the Owners Manual said to have the Alternator tested which I did...alternator was fine but Red light stayed ON.

I removed the Bat Temp Sensor and measured its resistance at room temperature and then placed it on a an incandescent light bulb and saw the resistance go up steadily as it warmed up.

However the ground supply to the sensor was missing so I added a ground and that fixed my problem.

So I agree that the Fan Relay my be faulty and could be replaced, you can test the Bat Temp Sensor is working and you can check for related DTCs.

You can download the 2002 Jeep KJ Service Manual here which is very useful to have in spite of some errors!

www.colorado4wheel.com/manuals/Jeep/KJ/

 

[04Liberty]

Was the defroster on? Defroster uses the A/C compressor to dry out the windshield air; if the compressor is running, even for that, the fan will run.

 

[Bigmoe]

Was the defroster on? Defroster uses the A/C compressor to dry out the windshield air; if the compressor is running, even for that, the fan will run.

BINGO! I turned the heat control knob to Off and the cooling fan is not on. Turned it to floor - no fan. Turned it to defrost and fan comes on. So I guess it's operating as it should.