LWechterPA

I have a 1999 Jeep Cherokee Sport 4.0 auto, A/C 167K on odometer and the electric fan continues to run after the key is powered down. Its not overheating (210 degrees-normal operating temperature in South Florida) new water pump, belt & HD Radiator. I move the key from off to "on" and "off" again and the fan shuts off. Any thoughts to where I should be looking for a fix? I have gotten use to doing this "routine", but occasionally the kids or wife use the Jeep. Another Jeep owner asked me I ever shut the A/C off by the switch? Answer is never. Any assistance in this forum would be helpful. You guys have saved me lots of $$$ over the last 7 years of ownership. Thanks in advance for your opinions.

dave1123

Now you see, that's funny. Because of my experience with aircraft, I always power down all the accessories before turning off the engine. It's just force of habit. That way there isn't as much load on the circuits on startup.

jordan96xj

Probably the most basic thing comes to mind is that the aux fan relay in the PDC (Power Distribution Center) is switching on, but sticking, and not switching off under normal conditions. There are other things it could be, but this would be a quick thing to check.

I would think this even more likely if you said that sometimes you have to switch the ignition on/off more than one time to get it to turn off the fan.

I would imagine that the 99 also is a little more hooked into the computer, and the computer probably has the authority to keep the fan running after engine shutdown. But I don't know for sure (I have a 96 that is a bit more basic).

In any case, I would still check the relay just to be sure that it is not malfunctioning.

CCKen

I do the same thing. Always have.


Aircraft mechanic 43 years.

dave1123

US NAVY Aviation Machinist Mate Reciprocating + flew MANY hours with my Dad.

XJRed96

Have you ever let the fan run and see how long it stays on? If you turned off the engine while the fan was cooling the condenser for AC purposes it may still be reading a relatively high pressure/temp and the ecm may be set to a timer to turn off after about 20 to 30 seconds potentially as high as 90 seconds. By turning the key back on the system reads that the pressure has dropped and turns the fan off, but it doesn't monitor the temp when it's in auto cool down mode. I can't verify this 100% but many other vehicles do this. Volvos go so far as to turn on the interior blower motor on after the car has been parked for 45 minutes if humidity is high enough so that it can dry out and as they put it "de-mildew" the evaporator.

Also it's possible that as mentioned you have a sticking relay. You can try swapping the relay with another and seeing if that remedies the problem. if it does I would suggest replacing the relay.

LWechterPA

The fan will run much longer than necessary (10-15 minutes) before I shut it off by the ignition switch. Fan will keep running even after a short drive and not up to operating temperature.

XJRed96

yea that doesn't seem like a timer function. try switching relays around and see if that stops the problem.

CCKen

If you have your AC tuned on the fan will run. If it's not on, the PCM may be getting a request for AC somehow.

XJRed96

This is what I thought but under normal conditions the PCM wouldn't command the fan on for more than a couple minutes. He has mentioned it'll be running 15 minutes after shut off and he has to shut it off by cycling the key which is too long for any timer functions.

OP mentions that it happens even if the Jeep isn't up to operating temp which again brings us back around to likely being related to the AC system.

Have you swapped Relays around at all yet?

LWechterPA

I have a Jeep buddy that has a 1999 Jeep Cherokee that I have been getting parts off of. I'll try and grab a relay from that one (blown engine). Update you by the weekend. Thanks for the assistance. Does anyone have a picture or diagram of which relay I have to switch out?

CCKen

You really can't swap relays with the fan relay. As you can see all the relays common to the fan relay are required to run the engine. You'll just have to replace it. Make sure the pin cavities for the relay in the PDC are not corroded (black) or are not pushed down in to the PDC.
.

LWechterPA

So i'm replacing the radiator fan relay to the left of your pic?

CCKen

Yes.

investinwaffles

I think I paid $9 for my fan relay from Advance Auto. Pretty cheap and still works after a year or two