QuestionHey Doug -
Only overheats when a/c is on and vehicle is idleing for period of time. Definitely due to electric fan not coming on. The item I'm looking for is the sensor that sends current to the fan.Was told it's behind front bumper, but don't see it. Any ideas? Thx
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Followup To
Question -
Fan will not come on.Connected directly to battery and fan works. Where is the relay switch and how do you replace it. Removed front bumper and headlight but still don't see switch.Thx.
Answer -
Well, are you overheating? The 4.0L should have a belt driven fan for engine cooling and the other only comes on for a/c or overheating conditions. The fan should almost slide right out from the top.
The relay you're looking for is in the same black box as the fuses next to your battery. It's fed by a 40 amp fuse (#5) in the box itself.
If you're having an overheating problem you may have a bad water pump or a clogged radiator. If your coolant looks like Rust I would suspicious of both. If you're overheating do to a lack of coolant remove the oil cap and check for a crack in the head straight down from the cap (coil rail ignition only, not 4.0L's equipped with a distributor).
Doug
AnswerThe power for the fan is sent via the relay in the Power Distribution center. Ground (g106) is provided through wires leading to either the left fender or the left frame rail. Either of which will be between the computer and the brake booster area. The power for the fan relay CONTROLLED side is fed directly from a fuse inside the PDC.
The Fan CONTROLLER side of the relay has power provided from the ignition switch start run-position and ground is provided through the powertrain control module. When the computer senses the a/c is turned on then it will complete the path to ground for the CONTROLLER side thus energizing the relay. With the relay energized the power side of the CONTROLLED side will then be complete giving the fan power and making it run.
At this point I need to ask a few more questions. The person who is telling you to look outside of the PDC... are they thinking this is like every other chrysler product with an external relay? Jeep Cherokees do NOT use external relays. Also, is this a true CHEROKEE or is it actually a GRAND CHEROKEE? Because there is a huge difference and I'll have to go to a whole different set of diagrams. The GRAND CHEROKEE DOES use an external relay which is mounted on the passenger side frame-rail area. I can't remember if the battery is on the pass. side or not but I know the last time a co-worker had to replace one he said it was hard to see and even harder to plug in my known good relay to see if the old one is bad or not.
So... which model and which engine do you have?
Thanks,
Doug
