Auxilary fan isn't working

I searched and read this thread:
http://www.naxja.org/forum/showthread.php?t=86802
and this one:
http://www.naxja.org/forum/showthread.php?t=87500

Both of them were very informative. And based on what I read, I figured my problem would for sure be the temperature sensor in the thermostat housing. So, I replaced that last night. It still isn't working though.

It's a '92 4.0L. The fan comes on when I turn the A/C on, but it won't come on by itself when the temp gets above 220. Is it correct that the relay is working fine if the fan works along with the A/C?

Would a bad thermostat cause this to happen? I haven't tried replacing that yet....and I have a new one at home.

My temperature inside the cab seems to be reading accurately, so I don't know that the temperature sending unit would have anything to do with it.

I'd prefer to NOT have a manual override switch. I'd like to fix the problem and then install the switch later.....if I feel the need.

Let me know if you guys have any other suggestions.

I just did this dance last week during my "vacation". I fried the aux fan on the way to St. Louis. When I found one at a yard and installed it, I got nothing. I did find that the giant 30amp fuse in the engine fuse panel was fried. I replaced that and still had nothing. Now when I turned the A/C on the aux fan would run.

From reading the wiring schematic, it looked, to me like the fan was powered directly by the ECU and that swtch in the t stat housing was merely a communication device for the 2. I even shut off the motor and then took a torch and heated the housing up to try and get that switch hot and trigger the fan. Nothing. I assumed that I was going to have to do a manual switch.

I took it for a test ride and temps were great (~210) with A/C on. Without A/C they really didn't rise that much but the aux fan never kicked on. Then I went into downtown and sat in traffic for a while...stop and go...and all of a sudden I heard it kick on. I jumped out and popped the hood and sure enough it was running. The needle on the gauge was on the white line between 210 and the red zone. Seems high to me and I don't recall the fan coming on that late before. Who the hell knows how accurate the gauge is though.

This probably doesn't help you much Brian but at least it lets you know my situation and what I tried. Good luck.

I should also mention that I did water pump, t stat, housing, hoses, CSF rad all within the last year. There really isn't too many reasons why I should be hot or having issues.

Thanks for the input....not much help, but it's nice to know I'm not the only one.

I did read this....it's a good way to tell whether or not the temperature sensor is doing what it is supposed to:
http://www.autozone.com/servlet/UiB..._us/0900823d/80/15/1c/7f/0900823d80151c7f.jsp

I wish I would have read that before I dropped $20 on new one that I probably didn't need.

I have the same problem on my '90 with open conversion. Works the first hot up, works with A/C, won't work on the next hot cycle on its own. Tap the relay and it starts up. I've replaced everything - temp sensor, relay, t-stat, pump, radiator, etc as each went out, and now it's doing this. It seemed to work before.

I was delivering rural mail when I noticed the fan wouldn't work and finally just shoved a 20 amp fuse spice into the relay socket to get it going. The '90FSM shows two diodes in the wiring harness to protect the A/C and Temp sensor from each other - I suspect the temp sensor one may be bad.

I just haven't gotten around to checking it.

Replace the fan swith in the radiator (driver side half way down ) this controls the elec. fan the relay is a by pass for the the AC and computer.
Best of luck !!!

Isn't that just another sensor? Or is it actually a switch? Is there a way for me to check to see if it is working before I just go buy a new one?

NO!
This only applys to the old Renix system.HO engines have the sensor located in the thermostat housing.Remember that the temp sender for the guage/light is in the back of the head.And the sensor for the fan is on the other end of the motor. I,m sure the temp readings are different between the two.
Wayne

xj4life2 said:

Replace the fan swith in the radiator (driver side half way down ) this controls the elec. fan the relay is a by pass for the the AC and computer.
Best of luck !!!

Click to expand...

Well, I just went out and started the thing up to see if the fan would kick on once it got too warm. It wouldn't get over the 220 mark just sitting there though....so, the fan wouldn't kick on anyway.

I did unplug the temperature sensor in the thermostat housing to see what would happen and the fan kicked on within a couple of seconds. I plugged it back in and it went off. That would indicate that the relay and wiring is all working the way it should, right?

Do you think I just ended up with a new sensor that is already bad? I'll have to do the electrical test on it tonight when I get home.

When I went through the same thing, I figured out that I really couldn't get it over the 220 mark just idling in driveway. After you do have it idling for a while, unhook the temperature sensor connector and check the resistance at the sensor. If it's in the 600 ohms range (+- 50) it's probably working fine and just telling you that the temperature isn't yet over 220 (it’s just close). You’ve already proven that the wiring is fine via your unplugging test so I’d just check the ohms at the sensor itself. If it’s a new sensor, you’re probably fine. It’s very unlikely the new sensor is bad.

Ok, maybe someone can help me now. This is the old sensor I just took out last night. According to this writeup, if I have infinite resistance between one of the terminals and the metal body, then the sensor is bad.

Here are the two leads connected:


Here is what I get when I touch one terminal (either one didn't matter) and the body:


And this is what I get when I touch the two terminals:


That would seem to indicate to me that the sensor is bad....according the autozone site. The new one in the vehicle is the exact same except when I touch the two terminals.....it shows as if I have the two leads connected....so, zero resistance.

Thoughts?

Proper test is with a digital ohm meter.From the FSM" The Resistance when measured across the sensor terminals with the engine warm should read 1340 ohms.
I,ll just list the ohms at the top operating temps-
temp min max
194 860 970
212 640 720
230 480 540
248 370 410
Replace sensor if not within range
Wayne

I'm getting zero resistance out of the new sensor at normal operating temperature (~210). I'm going to see if I can get a new one from Napa today. Thanks for posting the numbers.

Damn....I know I need a digital multimeter....this one has served me well on the trails though.

So, I got a new one from Napa today. They took the last one back on "warranty". The new one didn't work either. :flamemad: I borrowed a digi multimeter from a friend and took the readings. I started out with the engine cold and warmed it up to operating temp. The sensor read about 1400 Ohms of resistance when it started and then slowly decreased until it got to operating temperature. However, at around 212-215 degrees it was reading about 960-980 Ohms. That's too high....and would indicate that the vehicle would need to get even hotter before the fan would kick on.

I took that sensor out and put the original one in that I thought was bad. It was reading even higher than the new one. I'm going to take the new one back tomorrow and either get one from a different store or get their "upgraded" one.

What the hell is going on here?

What your finding is the reason so many have the same problem--fan not comming on at the correct temp.It seems that the QC dept is not on the ball.
Wayne

Can anyone tell me where the relay is for this fan? I'm going to replace it....even if I don't think I need a new one. Edit: I found the relay here and it clicks just fine when the fan goes on....either during A/C or when the sensor is unplugged:



I'm at a loss here. I'm on my 3rd sensor. This one is from AutoZone and seems to be at least putting out the right readings. The fan is still being a stubborn bastard though and not working. :flamemad:

If the relay doesn't fix it, then I really don't know what else to do. I guess I'll be wiring in that manual switch. I really didn't want to have to think about when the vehicle was getting hot though. I'll have to constantly watch the temperature gauge.....which is a pain in my arse.

if u are running a xj w/ a 4.0, it seems to be a given that the stock cooling system doesnt always keep the temp down (big motor jammed in a small space) i've been told over and over again to watch the water temp. because they will overheat. i just wired in a switch with an inline fuse, and plugged it into one of the open accesory slots in the fuse panel. this also serves as an idiot proof measure, as the fan will turn off with the key if i forget to flip the switch. all u need is some wire, a two prong switch, some connectors, fuse, and 20 minutes. it will make a world of difference, and i bet in the long run you'll like the manuel control