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Auxillary fan will not shut off.

Old 09-16-2016, 09:40 AM
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Default Auxillary fan will not shut off.

Hi gang, I have owned Jeeps from my first in 1976 straight through till today, I have had problems with the aux fans before, but always not working. Yesterday my aux fan would not turn off! I had to disconnect the battery cable. Searching the Forum it sounds like it could be the fan relay or the temp sensor. The temp here was 75 degrees and the temp gauge was normal at about 220. She is a 1999 GC, 4.0 with air, 188,669 miles. Thanks for any help, Mike.
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Old 09-16-2016, 04:37 PM
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Welcome to CF!

It sounds to me like a shorted fan relay. There is a 2-wire plug on the battery side of the fan housing to disconnect the fan. The relay is fed it's trigger signal from the PCM as a time-pulsed voltage, but the relay output is a constant 12v and on mine is only hot with ignition on.

My fan is also the only one I've got. There's no "aux" about it. Is yours stock, or did somebody add a clutch fan and rewire the electric one? IDK what the tow package setup is like.

There is also a high speed signal sent to the relay when the A/C is on. Some of the more expensive cars, like Mercedes, don't shut the fan off until the temp goes down, even though you shut off the engine. As far as I know, Jeep never used this.

In case you don't know where the relay is I have a picture;



When my fan relay failed, I wired in my own relay and switch until I could fix it, having it run on high any time the ignition was on unless I turned off the dash switch. That way I could turn it off on the highway and not risk burning out the fan.

Last edited by dave1123; 09-16-2016 at 04:51 PM.
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Old 09-17-2016, 12:33 PM
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Thanks Dave, I did replace my fan relay three years ago because the electric fan would not kick in, like you,cutting a hole behind the headlight. By auxiliary fan I mean the electric fan in front of the pulley driven fan from the engine. No tow package. I removed the 40 amp fuse so I can drive her around for now. I am going to replace the relay and see if that works. If a relay can fail open, I believe they could fail closed, letting the fan run constantly. Thanks for your input! Take care, Mike.
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Old 09-17-2016, 09:32 PM
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See, now that's interesting. My 2000 only has an electric fan, although the fan clutch hub is still there, that is the threaded boss. The only time I had an overheating problem was when that freaking relay died. As luck would have it, I had a piece of wire in my toolbox and ran a jumper to the PDC to get it home.
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Old 10-27-2016, 10:10 AM
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Sorry it has taken so long to get back. I finally got around to replacing the relay, it worked!!!! The fan quit running all the time. Thanks for the help! Take care, Mike.
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Old 10-27-2016, 05:06 PM
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I've noticed there are many fan setups on jeeps and it gets confusing why. Some have 2 and some only one and there seems to be no reason why. The clutchfan is totally inadequate for cooling in low speed, high temp situations, the electric fan seems to be fine in most situations just by itself, and the hydrofan was a good attempt gone bad!

My single electric fan works perfectly in any scenario, sitting and idling for long periods and staying within temp limits. Even creeping along in stalled traffic it's never overheated. My 4.0 has only gotten up to 240* twice, once when my fan relay quit and once when I got a pinhole in a heater hose. Even loaded with 1/2 ton of newspapers it's stayed within temp.

I WILL say however, that my A/C hasn't worked in 3 years. There's a leak in the evaporator and I won't tear the dash apart until I also need a heater core! My jeep has 201K miles on it.
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