From a couple pages ago (corrected slightly):

 

Checked this again today and got no low speed fan at 221F got high speed fan at 235F and still no low speed fan with the AC on.

So I am thinking low speed fan needs the resistor fix. I will do your fan check with the jumpers just to be sure before I do the resistor.

The car is registering it's correct temps so I don't believe it would be the sensor.

Thank you for all your help, let you know how it comes out after I get the resistor.

 

Just to try to set things straight. There is not a separate high-speed fan and low-speed fan. There is only one fan. It is made to run at a lower speed by connecting a resistor in series between the battery supply and the fan. This resistor is sized so as to drop the voltage supplied to the fan to about one half of the battery voltage.

The common failure is that the resistor fails open circuit, so that there is no supply to the fan when it should be running in the low-speed mode.

 

Thank you, yes, one fan 2 speeds, low going through the resistor. Bad wording, sorry

 

I have made current measurements of my 4 month old OEM fan on '04 S. On high speed there is a start up current of about 43 amps which settles out to about 21 amps once the fan is up to speed. Then to get the low speed current I used three, one ohm, 25watt sand resistors (just for testing) in parallel to get .33 ohms and put that in series with the high speed circuit. Low speed runs at 12.5 amps. once up to speed, start up surge is a bit over 20amps. I did this so as to know what power dissipation the series resistor would actually have. I did not find in this thread any actual measurements just speculations. Measurements were done using a .01 ohm 1% current sensing resistor in series with the fan. I pulled the high speed relay and jumper'd in the sense resistor with spade lugs.
You may ask why the 50 amp and 30 amp fuses if the running currents are so low? You need to accommodate the start up current and not stress the fuses during constant current conditions. Remember fuses get hot as they approach their rating and the resistance goes up, this is not what you want in any circuit. So fuse value is often twice the operating current as is the current rating of the wire on the circuit. The fuse is mostly to protect against the wire burning up if it goes into an over current state.
So at 12.5 amps and .33 ohms the resistor will dissipate 52 watts. The Arcol 100 watt rating is at 25 deg C with heat sink, 30 watts free air. Under hood may get to 70 or higher where I am in SoCal. At a 1 deg C rise per watt that's 52 plus 70 for a resistor temp of 122 deg C. IF it is well heat sunk. The spec sheet gives a max resistor temp of 200 deg C. Then it goes poof! I am wary of the engine mount location as I do not like putting holes in something so critical and probably stressed. So I like the bumper mount solution the one guy came up with. I am going to use that method and make sure to get heat transfer compound between the bumper bracket and the resistor mounting plate as well as under the resistor. The bumper bracket is aluminium, welded to the aluminium bumper backing so provides a large heat sink that also has air flow over it.
Hope this was enlightening.
P.S. History: at 65k new fan installed due to low speed failure (warranty so no cost), 110K replacement failed, no warranty, $500+ P&L during regular service. 116k (5months) AGAIN FAILED. Part warranty but I get to pay labor $250. So I'm doing the resistor substitution.

 

Glad it worked out for you LAHills.
My resistor is still working fine btw.

 

I think some of you guys are over-thinking the temperature/mounting location. The Mouser resistor is rated at 392 degrees F. That is pretty freakin' hot. I live in central Florida and the resistor is doing fine after a summer of driving in stop-n-go traffic. I have not seen any posts where a Mouser resistor has failed due to heat (or anything else for that matter). For a heat sink to be effective, it must have a lot of surface area per mass. A motor mount, aluminum channel or anything that doesn't resemble something sprouting thin fins is not a heat sink. You would probably be better off mounting the resistor with stand-offs to allow some air flow underneath than bonding/bolting it to large, flat, thick surface. Just my $0.02.

 

Since Arcol rates the resistor at 30 watts free air, at 52 watts during low speed fan operation, the resistor is over stressed especially in hot weather. It will not fail quickly as it is a robust component, but without heat sink it is more likely to fail eventually just like the OEM and this is what we all want to avoid. Though I certainly think the OEM is an inferior part in any case. One reason the Arcol will hang in there without heat sink is that the fan will not always run on low speed, any time spent in high speed means no power through the resistor. As for heat sinks any large metal mass (in extreme, think of bolting the resistor to a cubic foot block of aluminium, at 52 watts it would never heat up), or a small one with fins, will act as a heat sink. It has to do with mass and or surface area to radiate heat. The motor mount strut has both large mass and a fair bit of surface area, the bumper bracket less mass but lots of surface area as it wraps right around to the four foot long aluminium back side of the bumper. The bumper bracket has air flow to boot. Either would be better than no heat sink. I am curious though if your post means your resistor is just suspended in free air?
In closing, at the beginning above I pointed out free air rating. At 30 watts, Arcol is basically saying the part will last indefinitely in 25 deg C air, it won't fail in just a short time if you go just a bit above that. Parts degrade at a non linear rate above their rated spec, so at twice rated dissipation maybe half life and at 4x dissipation maybe 1/10 life and at 10x dissipation maybe POOF in a minute or less.

 

LAHills, I guess I'm confused about why you think a 25 deg C temperature must be maintained. I think Mouser just chose that particular temp as a baseline for comparison or perhaps that is a common ambient temp for this type of resistor. The resistance will change as the resistor temp varies but so what if the fan spins a little faster or slower, no biggie. Mouser clearly states that 200 deg C must not be exceeded but I don't see it ever getting anywhere near that unless you mount it near the exhaust. I didn't see anything in the spec that would imply resistor life is shortened for various operating temps, only not to exceed the max.

Mouser's maximum spec for heat sink thickness is 3mm. That sounds to me like anything thicker than 3mm is probably ineffectual. I mounted mine on the sheet metal support that is close the connector for the fan. I wanted to mount it in the stock location but it would have rubbed against the radiator. If I had more time I would have hacked up the shroud to make it fit. That would be ideal since it would be exposed to a nice flow of air. The problem with the stock resistor is that the wound wires are exposed to the elements and they eventually fail.

 

Thanks, LAHills, for posting the data you obtained. It's good to know what the
actual current and power requirements are. I wonder what the oem resistor is
rated for - I doubt it's really designed to dissapate 50 watts in its not quite open air
stock location.

 

Sorry if I was not clear. You are correct that there is no need to keep the resistor at 25 C. The point is that at air temp of 25C/77F without a heat sink the resistor is rated for 30 watts. And yes 25C is a standard industry reference point. And the heat sink rating at 25 C is for the air temp at 25 C, not the heat sink. At higher air temp the rated power goes down with or without heat sink. The power dissipation in series with the fan is at least 50 watts. Under hood in summer is going to be way above 25C/77F. This resistor with it's resistive element encapsulated and thermally bonded in an aluminium body makes it more robust than the OEM. If you run this resistor above it's rating it will not suddenly blow, but it will have a shorter life span, in a non-linear fashion to power. This is true for all electrical components. So the point of a heat sink is to keep the resistor temp below the 200 C and preferably much lower. That way you can expect it will never fail for the life of the car.
Again the formula would be 50 watts= 50deg C rise above heat sink mounting surface when the heat sink has 995 sq/cm. Smaller heat sink will have higher rise. No heat sink will be much higher. The spec sheet does not give a thermal rise without heat sink. But I expect since the power rating difference with and without heat sink is over 3 to 1 (100watt/30watt), the thermal rise may be 3 times higher without heat sink. If so, then at an under hood temp of 50C/122F plus thermal rise of 150C (3 degC/watt) the resistor is at 200C if no heat sink is used.
And the heat sink thickness is a minimum not maximum. More mass/thickness/surface area the better.

 

Thanks for all the help here. Got mine done today and it works great!

 

Just got the Arcol installed. I was going to go with the bumper bracket mounting location but noticed an old CPU heat sink across the room. Looking around under the hood I finally found a place where it would fit. Next to the power brake diaphragm. Air flow wont be great but there is some isolation from engine heat in that little compartment. It does have a ventilation grate above it. After install and running the A/C for a while in the driveway, the resistor and heat sink were uncomfortable hot to touch but not burning up. And it is about 40C/104F today in my L.A. neighbourhood. I have attached a couple of pics of the job.

 

Are you powering the CPU heat sink fan? From what power source?

 

Yes, its a 12 volt fan. Just tapped off the Arcol resistor so it comes on with the coolant fan.

 

Wow, that's a neat solution.

 

Hi guys I was wondering if there's a way to plug in the resistor without taking out the fan shroud in the models with two plugs, mine is a 2002 S.

Thanks in advance

 

Wow, lots of energy on this problem. Look way back in this thread, by the dorman fan assembly that has a re-designed resistor. Spend 1.5 hr to put it in and find something else to do with your time...

 

Second thoughts on the rewiring. It just hit me the shroud relay will get reduced voltage from the new circuit in low speed mode and may chatter and not stay on. So it was a bad idea.

 

*LIKE*

 

What about this?
http://www.ebay.com/itm/Fits-03-08-M...92a3ae&vxp=mtr

 

still air cooled though...........

 

Is that a functional replacement for the resistor that's physically located at the fan itself for speed control?

Or is that simply the computer's on/off control relay located elsewhere?

 

By the way it looks it seems to be an aftermarket replacement for the entire module in the fan.

 

Is this the resistor i need to get the job done???

http://www.ebay.com/itm/Chassis-Moun...item4607ede5f0