[fb111]

The only way I can turn off my electric auxillary fans is by pulling fuse 31. They are running continuously on a stopped truck that is not overheating. I did a search on fans and only found questions pertaining to ones that do not work. How do I diagnose this problem?

 

[Jos Geuze]

Hi

Power to the fans is switched via relays 13 and 14. See page 222 of the ETM and they are switched by the AC dual pressure switch.

Remove the relays and see if they are ok. Is there power towards the relay? (Do they click imediately when put in place)
If yes check your pressure switch. Remove the spade connector on the pressure switch and check again.
In the diagram fuse 31 only stops the left fan and fuse 36 the right fan.

If it is only the left fan running signal could come from engine ecu that triggers the fan to work when engine temperature becomes too high. Signal could also come from this source. In this case it is relay 18 that is switching and relay 13 is not.

Good luck

Jos

 

[fb111]

Jos thanks for the info. It is just the left fan that is running. I can remove relays 13, 14 and 18 and it still continues to run. Only removing fuse 31 shuts it off.

 

[fb111]

Additionally my AC system works fine. No faults or open book in the display.

 

[Jos Geuze]

Hi

At page 221 of ETM you will see that positive feed to fan is direct via fuse 31. The earth wire is switched through relay 13 and relay 18 to earth completing the path for the current to run the fan.

In your case you have to find the wire 2 on connector 177 and wire 2 on connector 198 and check if there is no path to earth.
It seems that the wire is earthed somewhere causing your fan to run all the time. This could also be a fault that is inside the electromotor of the fan.

To start with troubleshooting. Disconnect wires and measure if you have connection to earth from the motor connector. If you have your motor has an earth fault and is most likely shot. If you do not have the earthfault in the motor then check the wires by disconnecting connector 177 and measure on the connector towards the motor if you have the earth path. If you have then disconnect connector 198 and measure again. If you have the eart fault in the wire from connector 177 to connector 198 hen replace the wire. If the problem is not here then it is in the fusebox.

Regards

Jos

 

[waveydavey]

My guess is you have nothing wrong:
the fans are not for the engine they are for the A/C condenser so the engine temperature won't make any difference, only to the viscous fan.

Open the windows, Press the A/C off button so the light is on (check the compressor is not turning if you really want to be sure) and leave it for a few minutes.
I suspect once the condenser doesn't need cooling the fans will stop.

 

[Jos Geuze]

Hi

From the ETM:

Condenser Fans
The HEVAC panel provides a signal normally at 12
volts for “off” condition and 0 volts for the “on”
condition, which in the case of petrol vehicles is fed
into the ECM and diesel vehicles directly onto the
coil of relay 18. In line is the Air–Conditioning
pressure switch 2, which turns the fans on/off.
When relay 18 is energised, it provides connection
between relays 13 and 14 (fan 1 and 2) in series or
parallel with each other. This is dependent upon the
state of the air–conditioning pressure switch 1.
For the petrol option, when the signal enters the
ECM, the ECM will switch the output on/off to the
fusebox. The ECM will switch the output on
sometimes for engine cooling reasons even though
the engine has been turned off.

Please note that there is a posibility to switch on the left fan for engine cooling. This is what I was referring to.
Your diagnosis that nothing is wrong does not hold water because the fans are switched via relays. The reply given after my first advice was that all relays can be removed but the fan keeps running. a clear sign that there is something wrong.

Regards

Jos

 

[fb111]

Jos you are the man. Read your diagnositic instructions and my first doubting thought was how the hell can a running fan be the problem. Well I removed the grill and sought to eliminate the fan from being the problem first, as you suggested. When I saw the terminals were the same for both fan I thought the simplest check would be to swap the wires and see what happens. Well I have a bad fan. When the wires were swapped the same fan continued to run. I don't know how many hours of scratching my head you saved me. The diagnosis took 5 minutes. Thanks again.
Fred

 

[viperover]

Nearly everything is negative switching on P38s, makes it a pain to solve problems...