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  #1  
Old 11-01-2011
Jim Magowan Jim Magowan is offline
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Default Fan clutch problem

I have been having a problem with engine overheating and found that the fan clutch was not working. Using the manual fan switch is necessary to control temperature.

Had a new sensor installed was told the problem was fixed. Engine overheated on the 4 mile trip home.

While running the engine to add coolant the fan started running. It turns out the clutch works just fine if the front ignition switch is off and the engine is running on the rear ignition switch. If the front ignition switch is turned on (regardless of how the rear switches are configured) the clutch disengages and the fan stops.

The most likely explanation anyone has been able to come up with is that there is a bad relay in the circuit.

I don't seem have anything that shows how the fan clutch circuitry is set up. Any information, including which relays are involved and where the are located would be greatly appreciated.
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Old 11-01-2011
oldmansax oldmansax is offline
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If you have the same hydraulic fan setup as I, the default for the clutch is engaged, meaning the fan turns. There is a fluid bypass valve on the reservoir that opens to disengage the fan clutch. It only has two wires. One is hot from the switch, the other goes to one side of the temperature sensor. The other side of the sensor goes to ground. Default on the sensor is closed, meaning the circuit is made, fan is off. If everything is working, electricity is applied to the bypass valve when you turn on the ignition switch & completes to ground through the cold sensor, which is made. When the engine heats up, the switch opens, interrupting the circuit so the bypass valve closes & engages the fan. It is setup this way so the fan is always engaged if there is no electricity.

Since yours is disengaged always with the front ignition switch on, the bypass valve has to be always powered to ground. On mine, both wires from the valve go to the back of the bus, (front of the engine) by the sensor, which is right out in the open. One connects to the sensor & one connects to a terminal that is hot when the ignition switch is on.

I would start by tracing the circuit from the valve to the sensor.

TOM
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Old 11-01-2011
Jim Magowan Jim Magowan is offline
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Tom,

Thanks for the info. I think it is very like that our fan is wired essentially hte same way. In any case it makes a lot of sense. The guys at the shop should be able to check this out relatively easily.
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Old 11-01-2011
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rwoody rwoody is offline
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no

a sp is wired for fan to come on with 0 air and rut off the switch

it is back asswards as far as normal trucks and equipment

i didn't design it but made my cummins sp the right way! with new 100 switch
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  #5  
Old 11-02-2011
Jim Magowan Jim Magowan is offline
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Woody,

Could you clarify what you mean by 0 air? Any detail you can give on how the SP is wired would be helpful. So far they guys here have not been able to figure out how the fan is wired.

When you say it is wired to run off the switch could you clarify. How it is wired (how the wires are run, if there are relays, etc where are they and what do they do? These guys have spent a lot of time trying to figure it out and haven't been able to get it working.

Since the fan operates correctly if the engine is run on the rear ignition switch and the front switch is turned off, but the fan stops if the front ignition is turned on, even if it is still running on the rear ignition, it seems that the front ignition turns off or cancels out whatever is making it work on the rear ignition.

I am confused. Is El Paso still TX? I thought it was MX. I guess I mistook an apology for a deed.
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Old 11-02-2011
oldmansax oldmansax is offline
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My mistake. I figured the SP was just a shorter PT without the tag....

It's a whole different setup???

My PT fan is all hydraulic, no air involved at all...

That said, on the heavy trucks I have had, the air clutch on the fan works basically the same way. The default is engaged. If air is applied to the clutch, it disengages. Air is applied through an electric air valve. Apply electricity, the valve opens & allows air to release the clutch. Remove electricity, the valve closes, removing air & the clutch engages. Usually the air valve is hot to one side as soon as the ignition switch is turned on. The ground side of the air valve is then used as the control circuit. It grounds through the sensor as the engine warms up, or through the fan override, or some systems also grounded if the AC was on and the AC condenser was in front of the radiator.
Obviously, on this type of system, the fan was engaged until air pressure built up because, even though the system was not calling for cooling, it needed air to release the clutch.

TOM
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Old 11-02-2011
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rwoody rwoody is offline
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jim there is a air switch on the frame rail pass side rear

they make them N.O.(normaly open) and N.C.(normaly closed) is how they sell them

simple power to switch with 1 going up ft to override

they might have installed a fan control switch wrong (it has 2 wires going to it)

i dont understand what they have done messing with the rear key but sounds like they got power off it to run fan instead of using factory power

bet they didnt know there is a switch on dash!!!!
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Just a Hobby Shop now-Bird Repairs upon Appt and my Schedule -USAR Retired
Pleasanton Tx 78064
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Old 11-02-2011
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rwoody rwoody is offline
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tom

on my sp it took air to turn on the fan---weird deal so if you were cold the fan did not run !

the default was opposite any old truck!


when i put the cummins in there i changed it to like a big truck and how you described!
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RWoody
2003 LX Single Slide Hauling Wood 5
2 miles east from Texas Highway 37-97
Just a Hobby Shop now-Bird Repairs upon Appt and my Schedule -USAR Retired
Pleasanton Tx 78064
Do not use PM... please use
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  #9  
Old 11-02-2011
oldmansax oldmansax is offline
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Quote:
Originally Posted by rwoody View Post
tom

on my sp it took air to turn on the fan---weird deal so if you were cold the fan did not run !

the default was opposite any old truck!


when i put the cummins in there i changed it to like a big truck and how you described!
Woody,

So what you're telling me is I have ANOTHER WEIRD THING DONE BASS ACKWARDS FROM WHAT I AM USED TO ON A TRUCK!!!

I'm gonna havta get a nother notebook!!!

TOM
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Old 11-02-2011
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rwoody rwoody is offline
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well i dont know if You do but Jim has and a SP is that way..seen 3 of them the same!
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RWoody
2003 LX Single Slide Hauling Wood 5
2 miles east from Texas Highway 37-97
Just a Hobby Shop now-Bird Repairs upon Appt and my Schedule -USAR Retired
Pleasanton Tx 78064
Do not use PM... please use
rwoody@fullnet.net
http://www.ebay.com/usr/woody19571

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