This makes no sense

Okay, this makes absolutely no sense and I've had two mechanically inclined friends of mine ride with me to verify that it is really happening and I'm not crazy. My clutch fan on my 95 4.0L, yes my clutch fan not my auxilary fan, only functions when I turn the air conditioning on. Its mechanical so it makes no sense to me. If I'm in traffic my XJ is starting to run warm when I don't have the a/c on, click on the a/c and you can totally hear the clutch fan roaring as I accelerate. If I turn off the a/c it instantaneously stops working and starts to slowly warm up but not over heat, just run at like 220-230. Its not the auxilary fan that kicks on with the a/c. That is a constant hum, this is definitely the clutch fan, it increases in sound as I accelerate and I had a mechanic friend of mine and my Dad who is extremely good with cars ride with me and we all agree that its the clutch fan. I had to make sure I wasn't crazy since it makes no sense. The only conclusion we have come to is that the extra resistance from the a/c compressor makes it engage. But why is it doing this? Its only six months old. Should I just take it back and get a new one or is there something else that can cause this. I have a new serpentine belt on there that is adjusted properly. This blows my mind and makes no sense to me. :dunno: :dunno: :dunno:

Dumb question time - how do you KNOW it's the mechanical fan and not the electrical - have you actually looked?

I ask simply because that electrical fan is noisy as Hell, and can be confused fo the clutch fan (which is quieter - no separate motor.) Recheck that and see...

The electrical fan has two engagement signals on a logical OR setup - the Air Condition Request Signal (overrides the fan operation to ON when present) and the Thermal Fan Switch Signal. If the TFS is shot, the electrical fan (and noise!) will only happen with the AirCon on.

Since it's a 95, I don't know how the fan leads will work for an auxiliary switch. But, I'd find the TFS and check it (boiling water and a fairly accurate thermometer) or check signals at the relay. Let me know what your max file size is for your email box, and I'll see if I can get some circuit diagrams to you.

Again, this sounds like a problem triggering the electrical fan, even though you think it's the mechanical. I really urge you to visually recheck to see what's going on under there, there may be a critical datum you have backwards and that will skew your troubleshooting results.

5-90

I'm inclined to agree with 5-90. The mechanical clutch fan should not make any noise.

If what you describe is indeed happening, I wonder if the engagement of the a/c compressor is somehow changing the tension in the serpentine belt enough to cause something elese to change. But if the serp belt were loose, I would expect a very loud squeal when the a/c clutch engages.

Dunno.

Eagle said:

But if the serp belt were loose, I would expect a very loud squeal when the a/c clutch engages.

Dunno.

Click to expand...

I certainly agree here - but, since it wasn't mentioned previously (and it would be a Gawd-awful racket if it were there...) I didn't see fit to mention it myself either. Anything that would cause enough tension to cure a slip would be announcing itself with a screech whenever it engaged for a few minutes.

Remember the noise you'd get from your P/S pump when V-belts were going bad? That's it. Believe me, you'd KNOW if that were the case...

5-90

I've noticed on my 98 when it first starts up in the moning, cold, the fan really roars for about 30 seconds and then quiets down but that roaring is there. I have also heard it and seen the fan speed change or rather what appears to be the fan speed change, the fan blade give that precessing look, when charging my A/C and can even cause it by blocking the air flow with a piece of cardboard across the radiator. It's kind of a check I use to test the fan clutch vs drilling that hole in the shroud and sticking a thermometer thru there. Oh, both TJ's do the same thing, noticed it after we did the belts and idlers one morning and fired it up for the first time that day.

The fan clutch on the late, unlamented '99 WJ would roar very loudly for the first 30 seconds or so every morning, then nothing for the rest of the day. Factory (not dealer) technician claimed it was because the silicone gel tended to settle to the bottom overnight, so the clutch was unbalanced when you first start the engine. Half a minute or so was enough to distribute the goo more evenly, after which it would stay quiet.

Sort of sounds like it makes sense -- except it doesn't explain why none of the fan clutches on any of my XJs ever did that.

I appreciate the responses and I'm happy to get responses from those who I did. I have asked a lot of questions here on and all three of you guys have given me good advise everytime so don't think I don't value your opinions, but its without a doubt the clutch fan that is turning on and off with the a/c in addition to the auxilary fan. The auxilary fan actually kicks on without the a/c too when the engine temp gets hot. Like I said it makes absolutely no sense and I was hoping, by a long shot, that someone could make sense of this for me.

BTW, i know what you are talking about with the clutch fan roaring on start up, I had a Blazer that did that and my exgirlfriends Blazer does it too. My fan clutch is not OEM, i got it at Carquest. Its really loud when it works, the OEM one was quiet.

You've certainly handed us a poser... Here's a couple more questions for you:

1) Did you manually test the fan clutch as described? I mention this to rule out the possibility of a defective unit (it's rare, but it happens...)

2) Have YOU YOURSELF visually verified what's going on? I ask this to make sure we are all on the same sheet of music here.

3) Belt tension is correct, and there are no hideous squealing noises, right? Fingernails on a chalkboard stuff?

I know these seem to be pretty obvious (and asinine, I'm sure) but I ask them as a means of confirmation. This is just wierd enough you should probably expect this sort of htings while we hammer it out...

5-90

I visually have checked it out and yes, the electric fan does make some noise but its not this noise. I do need to clarify one thing, the clutch fan is only noisy when accelerating at low speeds around town, you can't really hear it at idle. It makes quite a bit of racket, a loud whirring sound when accelerating with the a/c on. I don't really mind the noise that much because when its making that sound it cools very well and the engine runs much cooler (210 deg or slightly below all day long regardless of conditions). It sounds kinda like my old 2.8L Blazer's clutch fan did. You can hear the electric fan at idle, it makes a constant hum, but its a totally different sound than the clutch fan makes when its functioning properly. While I haven't put on of those guages on the serpentine belt its pretty darn tight. In the middle of the belt I can move it about an inch if I press hard on it.

I did the clutch fan resistance test on it, but I don't know how accurate that test is. It might be defective actually, it has equal resistance at hot and cold. It never freewheels though, it just has slight resistance on it hot or cold. it i give it a turn from the top it will go a few inches before stopping. I don't know what brand name it is, but I got it at Carquest last fall and I paid around $60 for it. Its under warrany, maybe I should dig up the receipt and take it back. I think it has a years warranty on it. It looks like its going to be a real PITA to get out of there though. When I installed it last time I had the radiator out so it was pretty easy.

I appreciate you guys' help, this one blows my mind.

Sounds like a defective fan clutch to me - perhaps it didn't get its full quota of fluid...

When stone cold, it should be fairly easy to turn the hub and disc in relation to each other - this is the first thing I check when I am handed the part. This checks for assembly and manufacturing errors on the metal parts.

When warm (you can use a hair dryer for this) there should be considerable difficulty in turning parts by hand. I usually heat the part with a hair dryer on HI for about 10 minutes and check that to be sure. If it's still easy, heat for another 5 minutes and recheck. If it's STILL easy, get another one.

There's a trick to removing the fan clutch - unbolt the top crossmemeber that retains the top edge of the radiator, and you will be able to tilt it forward about a half inch. If that doesn't do it, remove the crossmember entirely, and you'll pick up about two inches. That had damn well better do it, because otherwise the studs on the pully hub are too long or your fan clutch is IN the radiator! If you need new studs, or want to replace with bolts, the threads are 1/4-20. I think using 1/2" or 5/8" bolts will work nicely, but I haven't tried them yet...

5-90

I was reading online about clutch fans and there was a test for clutch fans that said when you first start your engine pop the hood and listen for a change in pitch from the clutch fan after about 30 sec or so. Like you guys were talking about. I did that and there is definitely no change in tone. The only change in ton is when the a/c compressor kicks on and off. When the compressor clicks and kicks on if you manaully rev the engine while under the hood you can hear the clutch fan making a lot of noise and moving the heck out of some air. When it clicks of it goes back to normal. This blows my mind and maks no sense.

5-90 said:

Sounds like a defective fan clutch to me - perhaps it didn't get its full quota of fluid...

When stone cold, it should be fairly easy to turn the hub and disc in relation to each other - this is the first thing I check when I am handed the part. This checks for assembly and manufacturing errors on the metal parts.

When warm (you can use a hair dryer for this) there should be considerable difficulty in turning parts by hand. I usually heat the part with a hair dryer on HI for about 10 minutes and check that to be sure. If it's still easy, heat for another 5 minutes and recheck. If it's STILL easy, get another one.

There's a trick to removing the fan clutch - unbolt the top crossmemeber that retains the top edge of the radiator, and you will be able to tilt it forward about a half inch. If that doesn't do it, remove the crossmember entirely, and you'll pick up about two inches. That had damn well better do it, because otherwise the studs on the pully hub are too long or your fan clutch is IN the radiator! If you need new studs, or want to replace with bolts, the threads are 1/4-20. I think using 1/2" or 5/8" bolts will work nicely, but I haven't tried them yet...

5-90

Click to expand...

I posted that last response right when you posted this one.

I think I'm going to take my fan clutch back this weekend when I have time, until then, I'll just have to use the a/c when I'm in traffic. Oh well, its starting to get hot outside anyway. I called carquest and they told me just to bring my receipt in and they'll honor the warranty. I appreciate the help, its got to be a defective fan clutch, its the only thing that makes sense. I'll let you know what happens after the new fan clutch.

You say its driving you crazy....my wife always chimes in and says that for me it doesn't take much gas because its a short trip. Make sure and follow up with the results. Maybe its been possesed and you are going to have to make a sacrifice to the rock gods :worship:

Maybe it is possessed, it's about the only thing that would explain it, lol. :roflmao: