robsjeep

My 1990 Radiator fan is not turning on with the thermal switch on the radiator, it does turn on with the Air Conditioner however.
I thought it was the thermal switch, so I bought a new one, and then decided to test the old one in a pot of hot water on the stove, the old one works fine.

So I dug deeper, See the wire diagram. See the photograph, note with the little orange colored Diode module. There is a Diode Assembly or Diode Module located between the thermal switch and the fan relay
I ohmed out the wires and they are good between the thermal switch connector and the diode module, and the diode module to the fan relay, BUT current does not pass thru the Diode Module, no matter which polarity I use on my ohm meter. (i.e. there is no continuity between the grey outer wire (from thermal switch) and orange outer wire (from the fan relay) on this module, no matter the polarity)

So where does one buy a new or good used diode module? I can seem to find one on the interwebnet.
Also does the wires pull out of the diode module, or are they permanently attached to the diode module, I dont want to pull them too much if they are not removable.
So where do I find on e of the Diode Modules?

Thanks in advanced for your suggestion


Orange fan diode for radiator fan, 1990 cj

Radiator fan diagram 1990 xj

Corky

I haven't actually worked on the module in question.. But I have rebuilt/replaced bad harness diodes that give it up... The easy way out is hopefully there's a simple replacement for your application, if not you'll need to know the rating of the original and buy a replacement diode that's equal or higher rating for the swap and rebuild your module... Think of a diode is a simple electric current one way "switch" which allows current to flow only one way...It will block any current from back feeding..If any component fails and sends a higher current/ohm signal to the diode it could very well burn it out..

cruiser54

Key ON, if you select AC, the cooling fan come on.

Key ON, unplug the Fan Switch from the radiator and jumper the contacts in the harness the fan doesn't come on?

Saudade

Yep, that diode separates the feeds to the fan relay. Just double checking but you sure you got the right contacts? I see A-B and C-B would show continuity. A-C would also show open either direction.
Another test you can do is simply to jump the thermal switch connector on the main harness side and see if the fan kicks on assuming everything else is still connected.

You can see the small lock tab on the diode assembly. There's a small plug in the end that comes out with the diodes. I tried to get mine apart once but it fought back too hard and I stopped rather than risk damaging it. I managed to find a spare on a salvage yard trip. I've never seen one for sale online.

cruiser54

That's what I'm saying. TEST by jumping the radiator fan switch contacts while unplugged. Verify what's really going on first.