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Axillary Fan does not kick on


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I bought this truck in February and am now noticing that the temperature likes to climb to the 3/4 mark on the full cluster when stopped.

 

It is a 1992 4.0. I replaced the temperature switch (for the gauges) and the temperature sender on the thermostat. The auxiliary fan does not come on. I know the fan works. When I disconnect the temperature sender, the fan comes on as well as a MIL.

 

The fan does not come on when I turn the dash selector to AC either. Granted the AC does not work and the compressor does not cycle.

 

I searched and did not find much information to troubleshoot the fan operation on a non-Renix engine, short of a toggle switch. What suggestions do you have for me to try, inspect, or replace? Thanks.

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I don't know how, but I am sure you can test the temp sender in the bottom of the rad can be checked. Also, have you checked fuses? Something else, don't trust the gauge to be accurate. I mean even thou it may read 220 it may only be 205 or something lower, before the fan gets the "juice" to turn on....

 

CW

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I don't know how, but I am sure you can test the temp sender in the bottom of the rad can be checked. Also, have you checked fuses? Something else, don't trust the gauge to be accurate. I mean even thou it may read 220 it may only be 205 or something lower, before the fan gets the "juice" to turn on....

 

CW

 

He has a H.O. The temp sensor is on the thermostat housing.

 

Have you check the relay for the fan?

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With the HO system, the relay would be my first thought too. If you have AC, the fan should come on immediately with the AC being turned on, so try that to see if the fan is working at all or just put direct power to the fan to be sure the motor is good.

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The fan does work. Albeit a little rough and noisy, but it works. It will come on when the Temperature sensor in the thermostat is unplugged. The fan does not come on when I turn the HVAC selector to AC.

 

Where is the fan relay on the HO? I will double check the fuses.

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The fan does work. Albeit a little rough and noisy, but it works. It will come on when the Temperature sensor in the thermostat is unplugged. The fan does not come on when I turn the HVAC selector to AC. Where is the fan relay on the HO? I will double check the fuses.

 

If your HO fan comes on when you disco the thermostat temp sensor, the aux fan relay in the PDC (Power Distribution Center, right side engine) is fine. It will not come on w. the A/C if the compressor doesn't cycle. Normally they come on at 218-224 degrees or so, too high IMHO. On the HOs it's easy to wire in an unused SPST dash switch to apply a ground to the correct ECU pin to turn the fan it on w/o altering it's normal operation. Shoot me a PM w. your email address and I'll send you a wiring diagram. I've had my 91 aux fan wired like this for years w. a dual electric fan setup.

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