99 XJ... replaced aux fan with a known working fan, and now it does not work??

Ok the fan blade was cracked on my 99 XJ and when you turn on the AC or the defroster the aux fan kicked on and made a horrible wobble/shudder sound.

So I replaced it with a known working fan out of my 97 XJ.

I plug everything in and go to turn the defroster on, and the aux fan does not come on at all. Tried switching to the AC and the same thing happens.

I checked the 40 amp fuse and replaced the relay. The fuse was good and the relay appeared to be good but I swapped it with a known good one and it still doesn't work.

I am incredibly frustrated right now. Does anyone have any ideas why my aux fan is not working now?

It did come on as it's supposed to when the fan with the broken blade was in there.

Jumper straight from the battery to the fan and make sure it is working.

joe_peters said:

Jumper straight from the battery to the fan and make sure it is working.

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It worked 5 minutes before I pulled it out of the 97.

If the fan is not bad (I will confirm by jumpering it) what else could the problem be?

Your wiring skills ? Seriously, re-check your work.

Tim_MN said:

Your wiring skills ? Seriously, re-check your work.

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Its pretty hard to screw up a wiring harness plug that only fits in one way....

90Pioneer said:

Its pretty hard to screw up a wiring harness plug that only fits in one way....

Click to expand...

Also I just put the fan back in the 97 and it works great. I'm stumped.

the fan should turn on automatically if you disco the cts plug--that'll verify that the fuse, relay, and wiring are good.

Check the relay, my 99 has gone through 2 aux fan relays in the past 2 years. ( don't buy it from advanced lol)

First rule of electrical troubleshooting.....when all reason fails, trust nothing and check the most basic things even if you checked them before.

Put the busted blade fan back in and see if there is still power on the plug.

My sons had an aux fan that wouldn't run. Jumpered to batt, ran. Unpluged the temp switch from thermostat housing, fan would run, so I know it would kick on when temp was high. Aux fan also runs when defrost mode is set. Defrost uses the air conditioner to 'well' defrost, traced it down to presure switch on a/c.