Auxiliary fan is temperamental...

I put an override switch on my aux fan so I can control when I want it to come on. Works great..... except for one goofy thing. I can get it to work great until the engine hits 220* then the fan shuts OFF. Power is still being supplied and has not been interrupted but fan won't run again until it cools off.

So I completely bypassed the wiring from the ECU and wired the fan direct to an independent relay and still get the same results :huh:. I thought maybe it was getting a thermal signal from the ECU to shut off. So being independent from any other signal, I'm assuming there's some type of thermal relay inside the fan??? Or does the plug that connects the fan to the ECU have a built-in thermal "switch"??

You don't tell us the year -- assume '94? I believe the '94 setup is same as '93 which I bypassed with a relay (control unit) and no problems. Bypassing is really simple for these years and there is no inherent reason for the fan to shut off at 220*. What is the supply for your + and - ? Are you depending on the original wiring for your ground connection? Are you sure the fan itself is in good condition?

Bottom line is if you are sure the fan is always getting power as measured with a meter or test light, then the fan is defective. And just to confirm, there is no thermal switch in the stock fan unit that would shut the fan off at 220*. After all, that is approximately when you expect the fan to come on in normal usage

Thanks for your reply. I upgraded the '94 fan with a '97 10 blade. about 2 years ago. My power supply is from the battery to a 30amp relay. GRD is the same location for other grounds on the firewall. I'm using NO original wiring. 12g from relay to the fan and 10g to the relay. When the fan shuts off, power is still supplied to the fan. After about 15 min. or so, when I turn the switch back on, the fan will start back up. Can't figure out why it's acting like there's a thermal "breaker". Guess I should replace the fan, but can't figure out why it's behaving like it is. Driving me nuts.

Sounds like an internal thermal overload in the fan motor or a winding that is opening when it is hot. Could also be a bearing getting tight when it runs for a while. Spin by hand when it shuts off and see if it is tight. Use an ohm meter to see if you have an open circuit between the two fan leads when it shuts off (disconnect from the vehicle wiring to do this). If the motor is receiving power when it shuts off you have some type of problem with the motor.

westvirginia24976 said:

Sounds like an internal thermal overload in the fan motor or a winding that is opening when it is hot.....

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That's what it's beginning to sound like, but seeing that I'm electrically challenged, it doesn't follow my thinking of how electricity works in a motor. It's either burned out or it's not. Logic says that if the windings are bad, they don't mysteriously heal themselves when it cools off 20* - 30*. But like I said, how electricity flows isn't one of my strong points. I'm still questioning the factory connection near the fan. Pretty wimpy connecting contacts. Put some antioxydent gel just to see if that may be an issue. Nope.

I'll do some more testing like you suggested and see If I can narrow down the problem area.

Thanks for your suggestions.

"It's either burned out or it's not" is not exactly true. As westvirginia24976 said, a bearing can fail or a soldered or crimped connection can open when hot and close when cool.

If you haven't already done so, you need to unplug the fan when it stops and probe the supply connector for ~12 to 13 volts. If you don't have a meter and don't expect to really get into the electrical side of the Jeep thing, you can get an adequate meter at Walmart or similar for ~$10 or so. Even if you are "absolutely" certain that you are getting power to a fan or any other similar component, you always start here because it is relatively easy. If you have current to the fan and it is not running, you know that some aspect of the fan is at fault. Again as suggested by westvirginia24976, you can probe the fan side of the connector with the continuity or ohms function of your meter to see if you have an open circuit. Probably more a learning exercise than anything else because if it's not running you probably just want to swap it out. Let us know what you find.

Certainly one would hope that a fan would last more than two years but I guess there is a reason they come with one year warranties. The original e-fan in my '93 failed about four years ago and I replaced it with a similar unit. I have since wished that I had upgraded to one of the newer fans that I understand are quieter and more efficient. Considering your experience perhaps I will just stay with my noisy old beast.

Well, Pelican, I took the fan out and check basic stuff like bearing noise / resistance. I also checked voltage and was 11.8v when it was running. Got the same reading at the relay. I then sprayed lots of LPS electrical contact cleaner through the holes in the back and blew it all out. After giving it a real once-over, I realized that my type of use (mostly trails) has drawn in a fair amount of dust through the radiator as well as through the vent slots in the fan motor. I can almost visualize what the inside of the motor may look like??? So maybe that's my culprit.... DIRT?? Haven't taken it out for a test run after putting back together to see if that cleaning has made a difference, but I'm pretty sure that all that dust over the last couple (3 at the most) of years hasn't been a good thing. Those A/C fans aren't meant to be used in that environment for extended periods of time like I've subjected it to. So I've ordered another one, and if my current one starts working as it should, I'll keep it in my Jeep as a spare and put the new one on.

If this turns out to be the problem, now I wonder how my Taurus fan will hold up?? Might have to think about keeping a spare handy.

Thanks guys for walking me through this frustrating dilemma.

Update: Cleaning did not help the problem. For some reason there's a thermal "switch" inside the fan motor that prevents current from flowing to where it's suppose to go when it gets (too?) hot. Rechecked voltage and was 13.2 about 6" from the motor. Don't know why I was reading a slightly lower number earlier??

Anyway thanks again Pelican and westvirginia24976

One thing I learned as I worked on my 96 XJ was that when the engine temp got to 220 the aux fan would kick on, so if you are using the ground on this circuit maybe it is getting a back feed of power. Try to bypass all the connections at the fan and give power straight to the fan after it had shut off. If this works then you know that your fan is good and you have a power problem. I put in a flow kooler high flow water pump and a 3 core radiator and made my own high flow thermostat housing all new hoses and a 180 degree thermostat in and man it runs awesome. I also did a new mechanical fan and left the electric aux fan connected the way it came from the factory. If I need it I just kick the heater to defrost and no air.

rockchucker said:

.......so if you are using the ground on this circuit maybe it is getting a back feed of power. Try to bypass all the connections at the fan and give power straight to the fan after it had shut off......

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I had explored that theory as well. Bypassed (disconnected) the hot / grd from the ECU to the fan and it still behaved the same way. Thought (like you said) I was getting some signal through the ECU ground. But it wasn't that.

I've read other posts that have a similar issue but never heard how they got it resolved. Fan would shut off at around 220*. Goofy, because that's when it's suppose to come on.

I narrowed it down to the fan motor, can't figure our why / how it would come back on when it cools down 20*-30*. Got to be an expansion / contraction thing somewhere.

Thanks for your input.

So did you try just sending power straight to the fan? The only reason I ask is I work with low voltage electrical and have fixed many goofy issues for mechanic friends when it came to 12volt systems. I would take two leads right off the battery and add a 15 amp breaker to the hot lead, then have the fan get hot on the XJ and shut off, jump out and pop your hood connect the power leads to the battery and then the fan and see if it really does not kick on then I would agree with you that the fan has issues. Try not to let the magic smoke out of the fan.

rockchucker said:

So did you try just sending power straight to the fan? ..........

Try not to let the magic smoke out of the fan.

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I hooked up the fan direct with no influence from the ECU. Made no difference.

I just hope that magic smoke doesn't escape and and excite the Gremlins that are just waiting for a "hit":greensmok to set them off on other electrical parts.

Well then sounds like you need to get a new fan then. They should be easy to find and not that pricey. Good luck man.

rockchucker said:

Well then sounds like you need to get a new fan then. They should be easy to find and not that pricey. Good luck man.

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I ordered a new one.

When something breaks, I either repair or replace it. However, when something behaves like this, it really bugs me. Works when it's cool but not when it's hot.

Appreciate all the input... doesn't sound like anyone else has had a similar problem so I could pin the tail on donkey.

I'm going to tear down the motor to see I see anything obvious as why it's doing this. :dunno:

UPDATE: Got the new fan installed today. Works as it should. Then I took apart the old one to see if I could find the problem. Well, low and behold, I found one of the 4 braided copper wires that was connected to one of the brushes was severed and touching ever so slightly. The brushes and commutator, as well as the bearings, are in good shape so I'll repair it and keep the motor for a spare. The new fan motor was made in Taiwan and my OEM fan was made in the U.S of A. I may just put the old one back on to make sure it's OK.

Glad you found it! I know this intermittent situation has been really bugging you.