Running Cooler

[CharlesS]

On my 98 XJ I used what the Jeep has installed....
Cut the blue wire going to the condensor fan, extend the wires slightly, purchase a Bosch 30A relay, run 10ga wire from the battery with 25A fuse inline and tie the two ends of the blue wire to lead 87 and the new 12V power source to 87a, install a switch to actuate the relay. The fan will work normally when the A/C is on and when you need the fan.... just flip the switch....
I originally was going to try to actuate the fan using the wiring installed, but discovered that you will throw a code or possibly burn up the ECM by putting a 12V source into it... The ECM operates on signal voltage less than 5V.

Charles

 

[bjoehandley]

I know this has been a while, but did the colder t-stat in the '97 and later cause the computer to throw any codes? As for teh fan I've been running with the air or defroster on to kick on the fan in my '98.

 

[Calata]

FYI
While your engine is running you can unplug the temp sensor at the thermo housing the fan will kick in. That's part of the control circuit for '91s and later, you could wire in a switch to cause this "open" in the circuit.

Then You'll have your check engine light on ( at least on 97+ models ).

The easiest thing to do is wire a switch with 2 wires into the engine compartment. Tap the wires into the same 2 wires that the temp sensor on the thermostat housing uses.

The above solution will work because the temp sensor is a variable resistored path to ground. When the switch 'closes' because it's sensed that the coolant temperature is hot enough, it completes a full path between both wires. It just so happens that the second wire goes back to the PCM as ground sensing.

To test the above, use a small wire paperclip and connect both wires together on the temp sensor from the back of the connector ( with the connector still installed on the sensor ). Make sure your jeep is running and the coolant is somewhat warm already. If you do this with a cold, fresh started engine, it will throw a check engine light on as a fault in the sensor.