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Electric Fan not kicking in

xj92

NAXJA Forum User
My electric fan does not turn on when the engine gets hot. I've suspected this for a while, and I did some testing yesterday, and I couldn't get the electric fan to kick on. It's plugged in and connected. What sensor determines this, one of the temp ones? Does that sensor determine other stuff too, so I can see if it is working? At what temp should the electric fan turn on? TIA.
 
How did you test the fan motor ? Does it actually turn on when you apply electricity ? The sensor that is screwed into the thermostat housing energizes the relay for the fan. While you are at it..... check the fan relay too !!! I may be stuck and not allowing the fan to come on.
 
I just tested it by getting the temp up in the Jeep. I haven't tried rigging it up directly to electricity yet to see if the motor is bad.
 
I'll try what you suggested. Thanks.
 
Electiric fan should come on at between 210 and 215. Not sure when Jeep changed it but the coolant temperature sensor for the 88 is located on the radiator on the driver's side. There's a relay that allows the electric fan to come on under 2 conditions... the temp exceeding 210-215 or whenever the A/C is on. If your Jeep is set up like mine check these components and you should find the problem.

While we're on the subject, looking at my wiring diagram for the Chief it looks like it is impossible for the electric fan to come on after the ignition is placed in the "off" position. I think I remember that mine used to come on after shuting it down though... After the engine rebuild and all the other stuff I had to do to keep the Chief on the road it doesn't anymore. Am I getting senile or did I mess something up?:confused:
 
xj92 ,Did you find a fix? my '90 is doing the same thing,turns on with ac but not at higher temp.Posting a solution you may have found would be appreciated.Thanks
 
I've been out of town for a couple days and haven't found a fix yet. I'll let you know what it was when I do. Mine doesn't come on with the A/C either though.
 
Yes please post results. Mine quit working, along w/ my AC. I'm suspecting relays.
 
xj92 said:
I've been out of town for a couple days and haven't found a fix yet. I'll let you know what it was when I do. Mine doesn't come on with the A/C either though.

I'm pretty sure that the electric fan should kick on when you turn on the A/C.

On a 93 (based on your sig) you've got 2 temp sensors. The one you DON'T need to worry about is on the top rear driver's side of the head, and it connects to the idiot light or the temp gauge. The other sensor is in the tstat gooseneck. This one is hooked up to the PCM, and controls electric fan, open/closed loop operation, etc.

If the electric fan isn't coming on with A/C, then I'd suspect fuse, relay or fan itself.
 
Whoa - is that right? The temp guage/idiot light sensor is on the drivers side of the head? I've been having problems with my guage and have only been messing with the sensor by the t-stat (new sensor, connector, etc.) Am I working in the wrong place?
BTW- I have replaced almost everything on my cooling sytem (w-pump, rad, t-stat, sensors, fluid.) and my electric fan almost NEVER comes on, except with A/C. I think it works fine, ie., my car doesn't get too hot to need it. I think it needs to get pretty hot to crank it on...?

- TJ
 
Minor caveat: I'm specifically talking about open, OBD-I 4.0ls. It may (or may not apply) to other models.

The sensor for the gauge and the sender for the idiot light are in the head, at the top rear driver's side. Single wire hookup (it grounds through the block) and you use a deep well socket.

The sensor for the PCM is on the front, in the tstat gooseneck.

TJ, you're describing normal operation of the electric fan. It's a supplemental, for when you need a little extra push, like high engine temp or running the A/C.

You can disconnect the sensor/sender at the rear of the head (NOT remove it!) without any ill effects; it's for display purposes only.
 
Got it. I tested the fan and it worked fine, so I then went to the fuse. That was it. I guess I should have tried the easiest first :)
 
The 20 amp fuse in the fuse block under the hood. Little yellow blade fuse in with all of the big ones under the hood. When you pull the cover off of the fuse block it has a diagram. I believe it's labeled as Auxiliary Fan or Aux Fan.
 
Are those two sensors (t-stat neck & guage sensor) the same part#? I am pretty sure I have the engine you are speaking of., 1991 4.0l HO. I put the sensor I bought (idiot lite) into the t-stat housing. Is it working properly there? (I'm guessing no) Is it screwing up my cooling system? If the one I bought is called the "temp sensor" what is the one in the t-stat housing called? I know I'm getting off the main topic but since you guys are already on it... thanks.
 
truckeejeeper said:
Are those two sensors (t-stat neck & guage sensor) the same part#? I am pretty sure I have the engine you are speaking of., 1991 4.0l HO. I put the sensor I bought (idiot lite) into the t-stat housing. Is it working properly there? (I'm guessing no) Is it screwing up my cooling system? If the one I bought is called the "temp sensor" what is the one in the t-stat housing called? I know I'm getting off the main topic but since you guys are already on it... thanks.

I never can remember what year the change from closed to open cooling occurred. I was referring to the open system, which has a pressure cap on the radiator and an unpressurized overflow bottle. The earlier closed system has a pressurized bottle with a pressure cap, the radiator doesn't even have one to the best of my knowledge.

Come to think of it, I *KNOW* the PCM sensor will be different than the idiot light sender. The idiot light sender is a simple on/off that controls the light. The PCM sensor needs to know what the engine temp is to turn on the fan, go to closed loop mode, etc. so it's a ranging sensor.

Spent the last few minutes going through AutoZone's online parts...... apparently the PCM coolant sensor, the idiot light coolant sender, and the gauge coolant sensor are 3 different part numbers.

I don't know if it's "screwing up" your cooling system, but it for sure isn't doing you any favors.

As far as what to ask for: if you get asked "do you have gauges or idiot lights?" that one will be for the rear of the head. If you don't get asked that, it's *PROBABLY* the one for the PCM.
 
The reason I asked about fix was I heated it up good,just to bottom of redline and fan did not kick in and I remember when it would kick on before it got that hot.Mine is the closed system with sensor in the radiator and gauge sensor on head,since it is working with AC and not by tempature then I should be checking the sensor in radiator.Hey did I just solve my own problem :confused: Naaaa cant be that easy.
 
Well, pulled 20mini fuse in box, still good, but replaced it anyways, no worky. Drove to autozone, borrowed 2 relays for fuse block for a/c and aux fan, still no worky. Any ideas? Neither have kicked on since this summer has started. I also noticed that on defrost, there is a hmming sound sometime from the vents when the fan is on low. I remember reading something about a vaccum line, correct? If this is the case, are the a/c and aux fan affected by vaccum lines also?

Adam
 
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