Aux Electric Fan not turning on

Hello,
I have an 87 XJ waggy. My auxiliary fan is not coming on when I turn on the AC or the temp gets over 210.

I have replaced the relay with a known good relay and it still does not work.

If I use a jumper wire where the relay plugs in I can force the fan to run.

I have tried messing with the temp sender wires to no effect. I jumped them together and left them open... still the fan won't run.

Any ideas?

Thanks,
Matt

just put the fan on a switch. best thing i ever did

Would realy prefer to have it switched automatically based on coolant temp if possible.

The A/C should power the relay, period. Why that doesn't is partly to blame, as that current is sent through a diode to pull it in. The thermal fan switch (not really a temp sender) also sends current to the same diode in the wiring harness to pull the relay in and power the fan. When it's working right, the diode prevents either circuit from receiving the others signal.

Check the A/C circuit to see what's up and why no current, and the same for the temp signal. The question is, is current being sent to the diode and relay, or not?

Great! Thanks for the tips.

I will try and trace wires and see if I can find the culprit...

TiRod... taking what you have said and combining it with some of my other search results I am thinking that the issue may be that the relay is not seeing power.

Here is some information I found on relays when researching the fan operation:
http://www.projectxj.com/mods/stocker/fan.switch.htm

Using a 4 prong automotive relay that you can get at
Radio Shack (or similar), wire it according to this:

#85 - Ground
#30 - Battery
#87 - Green wire on male side of fan connection
#86 - Switch inside the cab

If I understand correctly the supposition is the post #86 is not seeing voltage. If so I should be able to test for voltage at this location.

Thanks,
Matt

OK so on the stock relay #86 post is not seeing voltage under any conditions.

I am thinking I should install a switch after all... as I have no idea why I can't get voltage to that post.

Next step is to apply voltage to the #86 post and see if anything happens.

Not sure how the renix electronics are, but on the obd1&2s if you unplug the cts, the fan will come on automatically(safe mode and will be running a rich OL). If that does it then maybe it is a faulty cts. Does the renix have the sensor in the back of the head that provides the dash temp gauge(like 91-96s do)?

OK so in looking at the wiring diagram the black wire coming off of post 86 is supposed to be ground.

The orange wire to post 85 is supposed to carry 12v when either the air conditioner circuit tells it to OR the coolant temp sender does. This orange wire apparently has a short to ground.

As a first step I cut the orange wire and put a new wire with a switch on it from the fuse box. I tapped the hot side of the blower fuse in the fuse box and put a fuse in-line with the switch. This now runs to the orange wire on the relay and serves as manual override.

At a later point I will hook up the temp sender switch to the same orange wire on the relay. This will give me both automatic temperature based switching and a manual override.

Thanks for the help!

Sincerely,
Matt

This is the common way to wire a relay:

30- to battery preferably with fuse
87- to the positive cable of your accessory, in this case the fan
85- to ground
86- to switched power ( in this case if you are going to use a switch to manually work your fan, get a switched power source, run a cable to the switch to operate your fan and from the switch to the 86 post on the relay.-

HTH

XJ-PRO