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Cooling fan diode function etc...??

1990Pioneer

NAXJA Forum User
Location
Denver, Colorado
Hello all, it has been 7 months since my last confession ;) Seriously though, I had modded the XJ, worked out the bugs and she's been one of the most reliable vehicles I have ever owned. My question is this, what is the purpose of the orange diode that sits on the driver side behind the head light near the fender wall? The engine runs great, I just happened to notice that the auxiliary fan hasn't ran yet this summer! I ran power from the battery to check its operation, it runs great. The temperature switch that screws into the radiator is open line all the time, even after driving for 30 minutes in 90 weather. I just installed the switch befroe summer, it could be bad. I'm wondering what role the diode plays in all this? I removed the diode and connected the 3 wires directly to each other and the auxillary fans runs whenever the ignition is turned on, engine running or not. AC running or not. I already have a toggle switch ran to that corner but I personally prefer to let the switches and relays do their job, If anyone out there can tel me the ins and out on this diode I wit!ould appreciate
 
Photo? I have never seen one on the 87-89 rigs

3 possible issues I know of.

1. low liquid level in the radiator (air trapped in the top of the Renix radiator is very common if not filled properly.

2. Switch is bad, new or not.

3. The radiator is partly clogged, flow is too slow, and the coolant is too cold once it reaches the thermal fan switch.
 
The purpose of the diode is to keep the power from back feeding back down the other circuit that could drive the fan as well. So the temp sensor/switch can turn on the fan and the AC can turn on the fan as well.
 
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