gregi

My 99 XJ Radiator electric fan is not working and i need a bit of help to figure this one out please.
The fan does work when jumped to the battery so it is not the fan, I swapped relays around and checked the fuses. I got the jeep up to operating temp and checked the resistance at the sender unit in the thermostat housing it read 8.3 Ohms. So I think the sender unit is ok?
I did not check the volts on the wire from the PCM.
Does anyone know where the ground is for the fan?
Any help or tips appreciated. Thanks

Roler

There is a bit of info in threads on the forum.
Do you have AC? Does the fan come on when you select an AC setting?

At the fan relay, jump the 30 and 78 'recepticles' for the same number pins . If the fan comes on, you know the fan part of the relay circuit works.
The fact you make the fan come on when applying 12V tells you the ground for it is ok.

PCM provides ground for the coil side of the fan relay.

bluejeep2001

Even simpler, remove the connector on the sensor in the thermostat with the engine running. If the fan runs, then the wiring...fan...relay and pcm function normal. The fan should also run if ac turned on and the clutch engages.

gregi

The Jeep has AC but it has not worked in the 6 years I have owned it, I did turn it on to see if it made the fan work but nothing, I also disconnected the fan from the sensor in the thermostat housing with the key on and the fan did not work then either.
I guess it does appear like this is a wiring issue?
I know the fan works, when jumped directly to the battery, I swapped relays with the fuel pump relay, I will remove the thermostat today and probably swap the sensor with another one.
All suggestions appreciated, Thanks

Roler

I'm not sure if for the thermo sensor disconnect check the engine needs to be running- key on might not be enough.

You can join the other thread we have at the moment for a similar (if not same) issue with fan not coming on. If your AC isn't working, your fan won't come either when selecting an AC setting.
(See other thread regarding bluejeep2001's advice in that case)

Roler

Def simpler yes (although less fun)🤣👌🏼

bluejeep2001

The engine must be running to engage fan circuitry...if it doesn't come on running and sensor disconnected...you have a problem. Swapping sensors is useless at this point

gregi

Today I removed the thermostat to try to eliminate my heating up issue, I then explored for the problem. i began by removing the relay and checked for power going to the relay which there was, so I jumped the connection opposite the power into the relay with a jumper wire with the key on and the fan ran So I assume my problem is the sender.
I then rigged up a switch on the dash through another relay into the fan wire. I got the switch power from the cigarette lighter wire and ground wire and put the switch in where the cigarette lighter used to be, seems to work. Now need to order a sender and a thermostat.