Hi guys, i've got a 92 XJ. Trying to figure out why the electric fan won't come on with temp. Kicks on occasionally with ac, bypassed aux fan relay and kicks on fine there. Take it out wheeling and it depends entirely on the clutch fan. No codes from the obd Any ideas?

 

If I am not mistaken, the auxiliary electric fan will only kick on when the coolant temperature gets pretty high. Alot hotter than the average running temperature you will see during normal driving.

I'm sure someone else will be able to correct me or tell the specific temperature.

 

^^^ this is true.... it's only designed to come on once the coolant reaches a certain temp. You could however test the fan it's self to confirm it actually functions.

 

On a 92, you have two temp sensors. One controls the fan, the other controls the gauge. If your temp gauge is working, the other could still be faulty or failed. Might also be a flaky fan relay. It's in the PDC. Swap some relays around to test it.They are interchangeable.

 

I ended up wiring it to a switch. Never looked back.

 

Its supposed to kick on at 220 ish as measured from the sender in the t-stat or when you turn on the AC..if there is enough Freon to engage the compressor.... .a simple test for fan and relay is to disconnect the t-stat sender connector...the fan defaults to on after about 3 sec...in later models like my 01 it is only based on coolant temp. My ac fried a while back so I don't have a compressor so I jumpered out the fan-on terminals of the compressor hi-pressure connector so If I turn to an AC mode...the aux fan turns on

 

Any hints where the second sensor is? Temp up to 230ish while wheeling. I know the fan works, I was convinced it didnt until i heard it kick on with the ac. I guess it's driven purely by freon pressures? I'm used to fans that kick on with max ac regardless of pressure. I switched out aux fan relay with known working relays, no joy. Bypassed aux relay, fan kicks on. I assume something is not signaling the relay.

 

The sensor that controls the fan and provides the computer with temp data on your year model is the one in the thermostat housing. The one that controls the dash gauge is in the driver's side of the head towards the year. That one isn't as important as the one in the thermostat housing.

You can test that sensor using a multi-meter. Or you can try throwing parts at it. If the sensor is bad it will give the computer bad info as well and should (but not always) throw a code. The computer is what is actually turning the fan on based on info received from the coolant temp sensor.

 

Since 92 is obd 1 only way to test sender is remove it...drop in boiling water for 2 min and then read the resistance across connector pins

 

Don't bypass the relay...pull off the connector to the temp sender in the thermostat...if it turns on with the truck running then your temp sender is bad or not calibrated or your sender for the gauge is not matching the other sender...its tough to guestimate 223deg on the temp gauge but its a good way past the 210 mark. . The fan doesn't react to Freon pressure exactly but is wired in to the ac clutch engage circuit..if the clutch does not engage due to low pressure...it doesn't arm the fan on circut

 

I used an IR temp gun and tested it with the unit on the Jeep and it tested to what the chart called for based on IR temp gun readings.

 

me too.