Does anyone know where the (two) diodes for the cooling fan are located?
This is a 2001 Cherokee Sport with A/C and a 4.0 L engine
I'm looking for the ones for the cooling fan, not the one on the clutch coil.

 

The only reference to a diode module in my 2001 FSM is for the headlights. My Renix has a diode module for the cooling fan. Are you sure you have one?

What specifically are your issues?

 

For what its worth, the FSM for my 97 doesnt mention, nor show, any cooling fan diodes either. Just the fan motor, fan relay in the PDC, and 2 fuses. One in the PDC (40amp), and the other in the JB (20amp). And ground (g106, drivers inner fender next to the PCM).

*I Googled a bit and a cooling fan diode appears to be a Renix-era thing only.

 

My cooling fan condition is that the radiator fan will not
come on under any circumstances and as you can see from
the circuit description, it appears that a faulty diode(s)
seems to be the only reasonable explanation that fits the
symptoms of the inoperative fan, and that being the case
my problem seems to that no one knows where these diodes
are located ?
And, although I don't really need to know at this time,
where is the temperature gauge sending unit located?.
(it's not on the water outlet above the thermostat!)

And here is what I know for sure;

I can make the fan operate by connecting a hot wire to the #4
socket of the fan relay so the fan and all wiring beyond the relay is sound
I do have a hot wire at terminal #1 of the fan relay base
I do not have a hot wire at terminal #2 of the fan relay base
The fan will run if I plug in a good fan relay into the socket and
attach a hot wire jumper to the #2 pin of the relay (energizing the relay coil)
The radiator N/O temperature switch operates normally and closes at approx. 185 deg

So I know that the Radiator fan relay and all of the associated wiring is Good

Looking at the above cooling fan circuit drawing, current from the ignition switch passes through the (closed) Radiator Temperature switch (after the temp .reaches 190deg +/-), then forward through the diode (at "C to "B" ) thus energizing the cooling fan relay coil at "2" (which now has a ground at #5) and that closes the normally open fan contact points to close in the relay, sending the current on through #4 to the fan fan motor

Circuit description:
The second diode (to the left - at A) is polarized backwards in relation to the + polarity current coming from the ignition switch, so it is blocked by this (2nd) diode and cannot branch off to the A/C clutch circuit, and thank goodness, because if the diode at "A" was shorted - or installed backward it would cause a direct path (short circuit) to ground through the A/C clutch relay contacts, and they would likely fry - unless a fuse burned out before the contact points melted (not very likely)

Assume in this this scenario, that the A/C is off, the cooling fan will come on IF:
The current from the ignition switch is able to get through the 190deg temp switch., the diode at "C', and on to the top of relay/solenoid coil (at #2) and through the relay coil, at #5 to ground. Of course, this assumes a good relay, an operational fan motor, and that all interconnecting wiring is sound

For the fan to come on with the A/C running, everything before the diodes and the ignition switch is irrelevant, as the fan relay coil now gets its current from the A/C relay at terminal #1, forward through the lower left diode "A"and out connection "B" that now energizes the fan relay coil at relay Terminal #2, through to a ground at #5 and the coil closes the fan relay switch and the current flows out #4 from the cooling fan fuse link to start the motor

 

The 2001 cooling fan is only driven by temperature sensed at the sensor in the thermostat housing. AC does not override temp on an 01. If you disconnect the connector off the sensor it should run the fan if the truck is running. It will set a check engine light. The sensor should read between 650 and 700 ohm at 212 boiling...sadly with only 1 sensor there is no way to gauge its accuracy without sensor removal or a non contact thermometer...whose accuracy is also in question. Remove the sensor...you should drain some coolant..put the sensor mostly...not the upper electrical part in a pot of boiling water...guaranteed 212 except if you live in denver...then read the resistance across the 2 pins should be ballpark 650-700 ish 10 or 20 each way no problem. The 01 should not turn the fan on till around 220 ish temp...its farther up the gauge than you think that diagram you have is not for a 01...no jeep turns on fan below 215 and only below 00 has the ac override.

 

Note from DJ to Dale285

That diagram that you posted is for the Renix-era Cherokees

 

Note from DJ
I just noticed that original post was from 12-10-21