Dropping resistor

Great call Wiswind I removed the dropping resistor today and the wires were corroded off. I unplugged it and the new one comes tomorrow. Anyone that is missing there low fan operation and only running on high look to the dopping resistor. Check out Wiswinds General Information. Easy fix. I wish everything was that easy.

I have both the hanes manual and the ford repair cd and cannot find anything on a dropping resistor. I did find something on the cd under air conditioning called an A/C pressure Transducer which sends signals to the PCM and fits the description of the dropping resistor. My question, is the dropping resistor exclusive to the 95-98 model? or did Ford just change the name to A/C pressure transducer for 99-03 models? I have a 00 windstar with the 3.8L V6.

I cannot directly answer that....I DO have a couple of pictures posted that show the location of the radiator fan low speed dropping resistor, on my '96.....and you could look at that location and see if you have one there......
Of course.....if not....they could have just moved it.

I have been mentioning it because, after installing a auxillary transmission fluid cooler......I noticed (by feel) how cool the cooler was with the fans on.....and how hot it was with them off.
Now....one thing that is hard on the transmission......is stop and go traffic.....and.....the auxillary cooler does very little without the radiator fans ON.
Keeping my A/C on in stop and go traffic keeps my radiator fans ON at low speed......cooling my transmission fluid.
So.....it is my personal theory (I am not an authority by any means) that this little part (dropping resistor) is a factor in transmission life......make sure that this cheap (as compared to a transmission) part is working....and you transmission will thank you.

MARZBX157
Just looked in the Haynes manual and they say that there are relays for years after 97. They look to be buy the fuse box in the engine compartment. Bad picture. That doesnt mean that they still dont have the dropping resistor though. The relays in the 96 are incorporated in the ccrm. Look behind the pasenger headlight for a ceramic oval shaped piece.

wiswind
Got my dropping resistor today and installed it in about 5 minutes. I cant ever remember hearing the low speed fans. Thanks

Hopefully this thread will get more people to verify their low speed radiator fan operation....and fix it, if they are not ON all the time when the vehicle is sitting still with the A/C ON.
It is a super cheap way to help the transmission fluid stay cooler.

I checked the vehicle with the engine running and A/C on and the fans were working, but I still have to find where my dropping resistor actually is located.

MARZBX157
According to Hanes manual. I quote. On 1998 and later models, a CCRM is not used and the relays are sepeate units located at the engine compartment relay panel. The picture appears to show them on the outside of the box two of them. Hope this helps.

The dropping resistor is present on the '99 model ... and probably later ones .. even though it changes appearances somewhat. The relays, also always present, also did do some changes over the years ... by 2001 (IIRC) they became "just relays" (no longer special relay assemblies with unique mounting areas) ... located among the ones in the fuse box by the battery.

And it is a good point about how important the fans are for saving the transmissions.

I've considered installing a cabin located toggle switch, that would allow me to select a constant fan "hi speed on" whenever I'm caught in stop-and-go traffic or trailer towing.

I wonder if in my 95 this could be causing my engine to almost stall after the low fan's turn OFF.

What mechanisms are at work "in the action of" turning the low speed fan's off?

The signal to the relays that control the radiator fans (high or low speed) comes directly from the PCM.
The PCM "decides" when the fans are on or off....and at what speed.

12Ounce mentioned that the droping resistor is present on the 1999 model, and that it might look a little different. Can you in more detail explain where it is, and what appearence it may have?
Thanks
Daveran

wiswind et all,

what is the ford part number and what is this part called? I would like to keep that info in my files in the event the low speed fan stops running on my 2003 lx.

thanks,

mundy5

I have called Ford parts and tried to explain this rather obscure part to them, that it is a ceramic resistor, what it is supposed to do, and the general location of where it is supposed to be found. Ford USA gave me this part number XF2Z14A601AB and stated that it was $72 and had to be ordered in. I then used this number and called Ford Canada and they gave me a price of $92 Canadian for this part, yesterday after explaining the part to them they quoted me $185 Canadian. So Telling them Where it is, What it looks like, what it does appears to be the only route you can take to ensure the correct part and price quote. Haynes does mention this part, and states that it is in the radiator fan wiring harness, that's it, no description of what it looks like, what it does, how to test it for failure or how to replace it.
Daveran

I have called Ford parts and tried to explain this rather obscure part to them, that it is a ceramic resistor, what it is supposed to do, and the general location of where it is supposed to be found. Ford USA gave me this part number XF2Z14A601AB and stated that it was $72 and had to be ordered in. I then used this number and called Ford Canada and they gave me a price of $92 Canadian for this part, yesterday after explaining the part to them they quoted me $185 Canadian. So Telling them Where it is, What it looks like, what it does appears to be the only route you can take to ensure the correct part and price quote. Haynes does mention this part, and states that it is in the radiator fan wiring harness, that's it, no description of what it looks like, what it does, how to test it for failure or how to replace it.
Daveran

Daveran2008 - I have to wonder if that is the correct part or not because I cannot see a resistor costing that much unless there is something uniquely special about this dropping resistor unlike most other resistors. I'd have'm fax you an image if they can do it.

Thanks for the advice. Yes $185, and the revised price of $92 sounds quite excessive, but it is Ford after all. I think that I'll Scoure the wreckers first. If they fail by having the wire corrode off the ceramic body then that is a visible way of seeing the good ones from the bad.
Daveran

Daveran,... assuming you are working on a '99 or similar:

You may want to take off the front "bumper" and have a look. Not a big job. The resistor pack is under there somewhere (I saw it ... but I don't even remember which side) .. and you could a photo to send to whomever you are ordering the part from. ... and I suspect the resistor pack is repairable, it doesn't look that high-tech ... you may not need to order anything.

Daveran,... assuming you are working on a '99 or similar:

You may want to take off the front "bumper" and have a look. Not a big job. The resistor pack is under there somewhere (I saw it ... but I don't even remember which side) .. and you could a photo to send to whomever you are ordering the part from. ... and I suspect the resistor pack is repairable, it doesn't look that high-tech ... you may not need to order anything.

Daz even betta. lol

Also a thought - if corrosion is what causes these things to just "fall off" rather than just the resistor going bad perhaps surrounding it with RTV, liquid rubber (paint on with a brush), or that new spray on rubber I've seen (both at wal-mart auto) would be a good idea.

I don't know about you guys, but I get the vibe that this is one of those parts that is gonna go obselete sooner rather than later. I did a lil research on what a dropping resistor is exactly. I'm assuming that the fan's really only have 1 speed (high or full speed rather) and that this dropping resistor is a way to reduce electricity to the fans to create a low fan speed since a "dropping resistor" resists voltage only to a certain point.

This makes me think... how come a normal resistor like the kind you see on electronic boards couldn't be used in place of this weird clunky ceramic thing? What someone would need to do is test the resistance of a new one to figure out what other resistor we could use (in theory) unless the ceramic thingy also has something to do with heat which I doubt since it sits in a plastic seat.

Well, as I've been trying to fix this "almost stall problem" on my van it ALWAYS 100% of the time almost stalls as SOON as the low-speed fans turn OFF. Reading up on Wiswind's dropping resistor info finally made me go look whereas I'd been resisting (huh huh) to look at it in the past cause it was just too damn easy. Sure enough tonight I saw that the leads are all rusted/corroded and the dropping resistor (which looks like a narrow ceramic horseshow) and that it was also cracked in various places and pieces of it are off at the leads. As I was trying to think of it like an electrical engineer might... since the resistor is made of ceramic the more pieces of it that fall off the less resistance there is for the leads to run through. Perhaps when my fans are cutting OFF this less resistance amounts to an electrical surge or short or even a loss of voltage somewhere. Trouble is I don't know which, but I do know this thing is broke and has to do with fan speed operation.

I have verified that the part number XF2Z14A601AB daveran2008 shared is correct. I did an exhaustive search and here is where I found it the cheapest though I wouldn't doubt if you call 20 Ford places you could probably find it cheaper somewhere up North: http://www.forddirectonline.com/partlocator/index.cfm?siteid=214462 - Ford Direct Online selling it for $53.70 - I ordered mine tonight.

Not to replace, but to supplement the wonderful Windstar parts photo library Wiswind has put up for everyone here are some photos of my broken dropping resistor:
http://www.thinkrolland.com/images/externallylinked/WindstarLowFanDroppingResistor0001-smaller.jpg

http://www.thinkrolland.com/images/externallylinked/WindstarLowFanDroppingResistor0003-smaller.jpg

http://www.thinkrolland.com/images/externallylinked/WindstarLowFanDroppingResistor0005-smaller.jpg

http://www.thinkrolland.com/images/externallylinked/WindstarLowFanDroppingResistor0007-smaller.jpg

http://www.thinkrolland.com/images/externallylinked/WindstarLowFanDroppingResistor0008-smaller.jpg

http://www.thinkrolland.com/images/externallylinked/WindstarLowFanDroppingResistor0010-smaller.jpg


http://www.thinkrolland.com/images/externallylinked/WindstarLowFanDroppingResistor0011-smaller.jpg

I thank you for the great pictures and information.
Daveran

Those are good pictures. But I'm pretty sure your resistor does not look like the ones on my '99. (I will take a photo of mine when I install a larger tranny cooler ... in the not too distant future, I hope.)

Electrically the different model year resistors all have the same, simple task (You described it pretty well) ...They provide a reduced voltage to the fan motor for reduced speeds. This means they absorb electrical energy and must dissipate heat energy ... thus the locations "mounted in air".

Any suitable resistors obtained from Radio Shack, or the like, should work just as well. The resistors must be of proper value ... or Ohms ... to provide the intended speed reduction. Does anyone happen to know what this is??

They must also be able to dissipate the heat ... thus the resistors must be of a certain "wattage" value also. (Typical resistors on a radio or tv printed circuit board are 1/4 watt.) My '99's fans are protected by a 50 amp fuse ... therefore the total wattage supplied to the fan(s) and resistor pack is ... 50 amp X 12 volts ... 600 watts. The original resistors are probably rated at 250 or 300 watts. If you could find resistors rated at 500 watts, or higher, that would be even better. Higher wattage resistors will only mean they can handle the heat better ... probably be a little larger ... and probably cost a bit more.

Now all we need is the Ohm value(s). ???

EDIT; Corrected my math a bit.

Those are good pictures. But I'm pretty sure your resistor does not look like the ones on my '99. (I will take a photo of mine when I install a larger tranny cooler ... in the not too distant future, I hope.)

Electrically the different model year resistors all have the same, simple task (You described it pretty well) ...They provide a reduced voltage to the fan motor for reduced speeds. This means they absorb electrical energy and must dissipate heat energy ... thus the locations "mounted in air".

Any suitable resistors obtained from Radio Shack, or the like, should work just as well. The resistors must be of proper value ... or Ohms ... to provide the intended speed reduction. Does anyone happen to know what this is??

They must also be able to dissipate the heat ... thus the resistors must be of a certain "wattage" value also. (Typical resistors on a radio or tv printed circuit board are 1/4 watt.) My '99's fans are protected by a 50 amp fuse ... therefore the total wattage supplied to the fan(s) and resistor pack is ... 50 amp X 12 volts ... 60 watts. The original resistors are probably rated at 25 or 30 watts. If you could find resistors rated at 50 watts, or higher, that would be even better. Higher wattage resistors will only mean they can handle the heat better ... probably be a little larger ... and probably cost a bit more.

Now all we need is the Ohm value(s). ???
I'm going to measure the Ohm resistance of the BRAND NEW one I have coming and post it back. The order gets processed tomorrow when they open. The only thing that bothers me about the resistors at radioshack now that you mention the need to dissipate heat energy is I wonder if those ones do "dissipate heat energy". IE: More surface area = dissipate more heat energy.... and the ones at radioshack or that I was thinking of on electronics boards are smaller and with not much surface area at all. Still though it seems pretty ridiculous to me that this clunky thing exists on our vans. I'd be curious to see what is used on the 99's and up cause I may switch to it if the same fan motors/specs are used and if the 99's one isn't made of ceramic.

I was thinking about my idea of putting RTV all over the new one. I don't see why that wouldn't work to help keep it preserved over time. I'm sure the main element is electricity that degrades it over time, but its also exposed to outside temp/humidity daily which contributes to cracking it over time I'm sure. RTV isn't conductive so I wouldn't think that it would create more resistance.... but if its wearing a coat of RTV it would most definitly interfere with heat dissipation. Bummer. :( wa waaa lol

EDIT: Just saw your explanation of watts and more heat. Well since thats the case then GOOD. lol - If I can obtain the ohms from the brand new one this may give everyone a workaround or just let us know if we can use the 99 and up resistor.

Yes, the ohms values will be very important to others.

I didn't mean to imply that the resistors were THAT different on the '99. They are still ceramic ... but just simple straight square corner cubes ... not the rounded edged casting as in your photo.

I have seen such high wattage resistors on some very old electrical equipment. Don't expect to find such on the shelf at Radio Shack ... but probably something they could order.

I believe mine were similar to the wire-ended ones here:
.
http://www.heiresistors.com/ceramic.htm

I received a reply from Haynes regarding their lack of information on the Radiator Fan Dropping Resistor in their manual. They sent me two diagrams, one of the engine compartment, and one wiring diagram. The engine compartment diagram for the 99 Windstar shows the socket for the resistor is in front of the battery on the drivers side. Hope this helps others with same question.
Daveran

Hopefully the part will arrive this week. I'm trying to get them to give me the new tracking # for reshipment as they botched the first order completely.

I have the new resistor. I'll be posting a pic of it soon. I measured resistance of 0.0 ohm and other times consistently 0.3 ohm. I wasn't using the "Cont" setting which makes a continuous beep sound when testing the ohms. Don't think that makes a difference though beyond just the "beep".

EDIT: I tested with switching the probes using the regular ohm setting and I'm still able to get 0.00 ohm often and very rarely 0.3ohm. Then I switched it to Cont for the beep and ohm testing and sometimes it starts at 1.1 or .9 or .7 and works its way down "ALWAYS" to 0.3 ohm. Some of the time (like 1 out of 10 or 1 of 8) of tests I did with Cont resulted in 0.0ohm. Am I just seeing the "dropping resistance" possibly here? Anyone make sense of any of that?

The people of Ford Direct Online must be illiterate or simply not paying attention at all. This is the 2nd time in a row they have sent me the wrong part (regarding the radiator cap). Instead they sent me a WHEEL ORNAMENT!!!!! At least this time they sent me the correct resistor. So for this order we're 1 of 2 correct and overall both orders were botched. I have to send this damn thing back again now. I think I'm gonna just have them credit me for the rad cap because this is ridiculous.

EDIT2: Also note that there seems to be a "Resistor Asy" (assembly of course) part number as we said: XF2Z14A601AB and on the new porcelain resistor itself is a different number which may imply to me you can order the porcelain dealy by itself. The number on the porcelain resistor wouldn't probably be seen on broken ones cause of fallen off pieces: XF2H-8L603-AC and above that is a number IRC 0027 which I have no idea what that is. I just searched for XF2H-8L603-AC in Ford Direct Online's parts web site and it doesn't come up. So I guess we might have to order the assembly which bites because this new assembly looks useless for my year Windstar anyway.... although it does seem like this one would help dissipate heat better if I can mount it the way it came.

EDIT3: There is a 30A fuse (hope thats a fuse; dunno what else it would be marked 30A) molded into the wire leading to the left most plug/port on the connector (ie: if you are facing the connector plugs with the blue part at the bottom).

Ya'll think I should figure a way to put it in with the new bracket or just take it out of the new bracket? I looked and on my 95 the little tray that holds it elevates it slightly as well, but this new bracket of course elevates it a bit higher (heat dissipation).

http://www.thinkrolland.com/images/externallylinked/WindstarNewDroppingResistor-0003-smaller.jpg
http://www.thinkrolland.com/images/externallylinked/WindstarNewDroppingResistor-0004-smaller.jpg

I apologize for reviving an old thread, but I'd like to know if anyone identified the requirements for the resistor. When I was doing some recent work on my Windstar, I noticed that the resistor had failed (for the second time). Thinking along the same lines as searcherr & 12Ounce, I want to see if I could find the resistance and power handling of the Ford device and substitute a more permanant solution to the problem.

The big issue is the current handling (and therefor power dissipation) of the resistor. My initial guess is something around 200 watts power handling. The resistance is small < 0.1 ohms, but the current is large, so it needs to handle a large amount of power. The heat of the engine bay on a hot day has to be accounted for as well. You can get catalog resistors that will handle 50 watts, and a combination of several could be made to get to 200 watts power handling.

Does anyone know what ratings are required for the dropping resistor?

Apparently, Ford no longer sells replacements for this part. I called a few salvage yards, but no luck there. I did some testing on the resistor that failed, and determined the resistance to be 0.15 ohms.

FYI, you can't measure this resistance value with a standard DMM, because the contact resistance from the leads will swamp the resistance reading, and because the resolution of these meters is usually on 0.1 ohms. The only way to measure this value of resistance is to use a Kelvin resistance measurement.

The circuit this resistor is found in is fused by a 40 Amp fuse. Therefore, the maximum power dissipated in the resistor is Pdissipated = 40 * 40 * 0.15 = 240 watts.

I did some searching on-line, but could not find anything matching (or exceeding) this power rating. Ohmite makes a 0.1 ohm, 50 watts resistor, and six can be combined to make a 0.15 ohm equivalent resistor capabale of handling 300 watts.

The remaining problem to be solved is adequate cooling of the resistor (FYI, 300 watts a little less than 1/2 hp, so there is significant heat involved here) If the resistor is not kept cool, then the power handling will be reduced from the specification.

I just replaced a dropping resistor on a 2001 Windstar. I thought I would share a few pictures, as I couldn't seem to get a good answer on where it was located. I was told left side, behind bumper, by headlight... Turned out that I was able to get to it by removing screws around the left front wheel and fender, and opening a gap there, to access it and replace. On mine, the non-replaceable fuse in line with the resistor was open. I don't know why they did not just go with a two winding fan motor, rather than this heavy, expensive resistor??
Hope this helps someone...

@TheBill & @rlp71068
So... how is the resistor holding up? Is everything functioning as it should? 300w according to my math wasn't high enough. @40A @12V with .15☊ (according to someone above) should be around 480W, maybe 500W to be safe.

I don't know why there isn't an updated Ford procedure for this! Lack of detailed info also makes this job more difficult! Grrr.

And @TheBill, where did you pick yours up at? The windstar I'm working on is a 96... idk how compatible it would be with mine. I'm pulling my hair out trying to figure out a way to fix this the right way. Because the PCM controls the fans, a few ppl were telling me (and I agree due to the schematics I looked at) that I can't hard wire Key On relay system to it. Ford is useless. If a customer dropped off a vehicle for service, I don't see them saying, "sorry customer, you need a whole new van because this part is discontinued"

Ford must have a procedure to remedy this or a superceded part, IMO. Seems like it's a huge secret. Lol

Go to www.fordparts.com (http://www.fordparts.com) and put in your VIN to search. I believe it's a different part for Gen 1 (95-98) but I'm not sure. You'll see diagrams as to the exact location on fordparts.com as well. I think it's on the other side on earlier models. Good luck!

Yes, the vehicle I'm working on takes a different part number. The part I need is: F58Z14A601B
I already have it out of the vehicle. My dilemma is, I need a replacement one. Ford has discontinued making them. There are no aftermarket ones available. I used the site you posted, just for shits & giggles... & it told me what I already know: Part Discontinued. Contact my local dealers. I also tried looking for new, leftover stock... Amazon, Ebay, Craigslist, etc

My local dealers already told the part was discontinued... but nobody can give me the Ford procedure of ....
What does a Ford dealer do?? When a customer's vehicle comes in, and it turns out they need THIS part.... the part is discontinued... Do they tell the customer, " You need a new vehicle"... No, I highly doubt that. I've still been searching through other forums in the meantime, to no avail.

Try this. Better act fast!

http://www.ebay.com/itm/NEW-OEM-Ford-Resistor-Assembly-F58Z-14A601-A-Ford-Windstar-1995-1998-/161874194042?hash=item25b0742e7a:g:gf0AAOSwhcJWM6l G&vxp=mtr

Oh I saw that one.... but it's not OEM for sure. There are no specifications listed anywhere either, as far as resistance or watts. That was home made & last wk it was posted for almost $40. from the same seller, whom I also emailed. I don't think it's going anywhere too fast. Before I go throwing in a handmade part, I want to verify everything else. I also want to know what Ford does in these cases, as I stated above. The last thing I need is for the PCM to be burned up. I really appreciate your looking & your input though. Thank you.

It says it's a Ford genuine part. I don't think any company made that aftermarket. He's even got a picture of the ford bag it comes in. There is a money back guarantee, and the seller has an excellent feedback rating (6 negatives in 12 months is basically perfect.)

Your call, though. I'd go for it. I've ordered several OEM parts from ebay and have never had an issue.

Good luck!

Ive gotten many OEM parts off Ebay. I'm not knocking them or that. After going back to the page & comparing what I got & what they're selling, I remembered also why I didn't just buy it. The bracket is different & so is the connector. The part is from UK, so maybe only fits UK vehicles. The part #'s are slightly different also, mine ending in B, theirs in A. There are differences from vehicles here & there. So even I bought it, I'm still taking chances & have to change the connector. Again, rigging without the Ford values from the original or this one, scares me.
1st 2 images are of the one I removed:
https://www.dropbox.com/s/48cnqyu27w0wdl2/2016-08-05%2019.29.02.jpg?dl=0
https://www.dropbox.com/s/ankl2k6d2f46dwe/2016-08-05%2019.29.13.jpg?dl=0
This is the one from Ebay:
https://www.dropbox.com/s/zf0zhwpoqm1o9bw/2016-08-05%2023.31.42.png?dl=0

I see what you mean. It's definitely a different connector but that's due to different electrical standards in europe. You could easily swap that over or just replace the connector with a new one (those are available, interestingly enough). However, without knowing the specs on the resistor itself, you can't be sure it's the same part otherwise.

It might be time to visit a junkyard. You may find one in pretty good condition. I've been surprised by junkyards many times!

I have visited the yards... they are barren!. In the meantime, I'm still searching online, asking people, & checking responses. Now you see a little better what I'm going through. I also don't like taking risks on customer vehicles... or any vehicle for that matter. PCMs are pricey! lol

I will continue to touch base & when I do find an answer, I will post it!! Thanks for your input and help though!

So a few last quick things -

1. That connector in the pic on that ebay auction is for a fuel pump dropping resistor in other vehicles (I think the trucks like F-150's and such). Thus, if that picture is correct, it's definitely the wrong part.

2. You may want to ask the dealer parts guy/gal to pull all the models that carry that part. I'm pretty sure Tauruses and possibly other vehicles of the same vintage used the same part. It's worth a shot if you really come up empty.

3. You can always just connect the wires together and bypass the resistor altogether. You'l then only have high fan speed whenever the PCM calls for cooling. (Fan will NOT run constantly, though.) You may get a "coolant temp low" code and would definitely lose fuel economy in that case, but it would at least get you back on the road. If you only do local driving, it may not make a big deal. I drove a few hundred miles with a thermostat stuck open once and it was ok. :)

Good luck!

1. I did check with Taurus also.. yes some are the same. None to be found.
2. Oh I tried with a few different dealers... the parts people only do so much and aren't in the field. I am in the process of meeting up with one of my Ford Techs, just a matter of timing. We were supposed to meet up today, but we were both set back. I'll get his login info too, & then I can do even more research through the FoMoCo Site. Especially if he can't answer my questions or come up with a solution together.
3. I already know just connecting to 2 wires is a no-no. PCM drivers get whacky. It's a customer's vehicle, I do not do work that way. It will have to pass future State Inspections... I don't need repercussions down the road.

I'm the type to do it right the 1st time or the best possible job.
In 20+ yrs of wrenching I've literally only had 5 or 6 comebacks. Maybe 2 were for defective parts etc. I'm still working on other things in the meantime, and my customer prefers to have it done right too. 15+yrs with me. "Knows how I roll" lol :-)

1. I did check with Taurus also.. yes some are the same. None to be found.
2. Oh I tried with a few different dealers... the parts people only do so much and aren't in the field. I am in the process of meeting up with one of my Ford Techs, just a matter of timing. We were supposed to meet up today, but we were both set back. I'll get his login info too, & then I can do even more research through the FoMoCo Site. Especially if he can't answer my questions or come up with a solution together.
3. I already know just connecting to 2 wires is a no-no. PCM drivers get whacky. It's a customer's vehicle, I do not do work that way. It will have to pass future State Inspections... I don't need repercussions down the road.

I'm the type to do it right the 1st time or the best possible job.
In 20+ yrs of wrenching I've literally only had 5 or 6 comebacks. Maybe 2 were for defective parts etc. I'm still working on other things in the meantime, and my customer prefers to have it done right too. 15+yrs with me. &quot;Knows how I roll&quot; lol :-)

You seem to know a lot more and are a lot more experienced than I am at this stuff. I'm just a computer geek that fixes cars in his spare time. (And I know not to mess with anyone from Philly; I've sat with far too many Eagles fans in my life at Redskins games ;) ) Good luck!

You seem to know a lot more and are a lot more experienced than I am at this stuff.
It is my main source of income, so that may be an accurate statement... not that I claim to know it all either. You can learn something new everyday. lol I work on construction equipment as well as the small engines like landscaping.

I'm just a computer geek that fixes cars in his spare time
I do work on computers too & built a few. But i'm sure you're superior to me in that field. Now I may have a "go to" guy... hint, hint... :wink: lol

I know not to mess with anyone from Philly; I've sat with far too many Eagles fans in my life at Redskins games ;)
Surely can be a rowdy bunch... SMH. :rolleyes: I can't wait to get out of the city. Tired of the high crime, noise, & miserable people. Lol.

OK, this is very unconventional, but I have the same problem and have planned (but not carried out) to fix it this way...

As far as I can tell, the motor is being run through the resistor to reduce the voltage on the motor to about 6 volts. This is actually a brute force method in electronics, the way things used to be done.

A "better" approach is one that avoids the resistor, but switches (at a very fast rate) between fully "ON" and fully "OFF", at just the right proportion that the average voltage on the motor is the desired 6 volts. This a version of what they call a switching power supply.

Of course, this is definitely a hack, and there's no telling what kind of problems will be caused by implementing it improperly, anything from electrical noise that causes radio noise to PCM issues, over voltage conditions caused by turning the motor on/off at a rapid rate... more.

In the mean time, I turn off the A/C at stop lights, or even don't run it at all unless totally necessary or driving >50 mph.

I just took another look at my wiring diagram. On the '99, there is a low fan speed relay, that uses the dropping resistor, and a separate hi-fan-speed relay that feeds the same two fan motors a full system voltage. The relays are fused separately. Therefore if the fans are not coming on at all ... there is more wrong than just the dropping resistor. The hi-speed circuit should offer a separate cooling fan supply voltage not dependent on the dropping resistor.

Note: I apologize for the mis-leading math in one of my earlier postings ... I must have been smoking something very good!

Just a little help for those trying to calculate power dissipation for the OEM resistor...

Power dissipation for a resistor is the voltage drop across the resistor (not the supply voltage) times the current through the resistor.

Power = Voltage_drop * Current

Voltage drop for a resistor is resistance times current.

Voltage_drop = Resistance * Current

Therefor:
Power = (Resistance * Current ) * Current
Power = Resistance * (Current)^2
(e.g. P = I^2 * R)

Some comments have determined the voltage drop to be 6 volts. If the current is 40 or 50 amps, then the power dissipated is 240 watts to 300 watts (40A * 6 v or 50A * 6 v).

I measured the resistance to be 0.15 ohms. Also, my low speed fan circuit is fused for 40A maximum. Then the maximum voltage drop over the resistor is 6 volts (0.15 ohm * 40A) and the maximum dissipated power is 240 watts (6 v * 40A).

When you calculate power using the supply voltage (B+ or 12 v), then you've calculated the total power delivered to the resistor plus the fan motor. So, when the fan is running at low speed, if it draws 40A from the 12 v battery or alternator , then 480 watts ( 12v * 40A) are pulled from the electrical power source.

From the previous calculation, the resistor dissipates 240 watts and the fan consumes the remaining 240 watts. However since the fan motor is doing work moving air only a portion of the 240 watts is dissipated as heat in the motor.

... and just to supply some real "who cares" information: the resistance is somewhat dynamic, in that it will probably increase significantly with increasing temperatures. So who can say what the resistance is once heated up? (Anyone know how a thermistor works? I do. It was a freshman lab study eons ago.)

Back to my nap ...

So far the resistor in my 96 is good but if it was to die and no replacement is available I would look at putting the 2 motors in series for low speed. Should be able to do it with a couple Bosch relays.

Let the original High and low relays drive the added bosch relays and the PCM will not know the difference. Will have to drag out the manual to see how hard this would be to do.

000

Adding the circuitry to switch the motors from parallel to series operation should also work. It seems like a good work around.

I don't think the resistor changes very much, even if it gets really hot.

The dropping resistor is made from Nichrome, which can be engineered for a low temperature sensitivity by controlling the ratio of Nickel to Chrome. Typical resistors of this type have temperature coefficients of < 0.05%/degC. So, if the resistor heats up 200 degC (hot enough to melt solder), the temp change from ambient will be about 1%. That means your 0.15 ohm resistor is now a 0.1515 ohm resistor.

On the other hand thermistors are designed to have a large and predictable change with temperature. They also are normally designed for a resistance that falls with temperature (negative temperature coefficient) although thermistors are available that have a positive temperature coefficient. Thermistors have a large resistance change so that they are good temperature sensors (hence the name). The negative change ones are normally used in sensor applications, while the positive change ones are used for heater regulators or initial on current sources (such as the degaussing coil of a CRT).

And since it was asked, the type used for sensors are typically made from silicon (like a transistor) with one or more impurities added to control the resistance and rate of change. In layman's terms, as they heat up, the thermal energy activates more electrons to carry electrical current which lowers the resistance.

The type used in heaters are based on a different technology (and materials), that have a "critical" temperature where the resistance increases very rapidly.

In most conductors: higher temperatures, therefore higher electron activity, is associated with higher electrical resistance. Hence, "Super Conductors" would usually make very chilly bed mates.

Thermistors are often conducting globules, such as carbide particles, suspended in a semi-rigid non-conducting plastic potting material. As the temperature rises, even though the individual conductive particles increase in resistance ... the over-all resistance decreases; because the size of the particles increase, making more conductive paths and decreasing the contact resistance between particles as they pressed together with more force. As you write, this is all subject to selective design.

That's an interesting and unique approach. Do you know which manufacturers make them that way? I've only used the (NTC) semiconductor type, like that used for the engine coolant temperature sensors in the Windstar.

"I would look at putting the 2 motors in series for low speed"

I have a couple of thoughts.

Make sure the design works with the logic of the controls from the PCM. I don't recall if low speed and high speed are complementary (high speed is false when low speed is true, high speed is true when low speed is false). If not, then a different approach is need than how I've envisioned it ( a switch on the positive of one motor, a switch on the negative of the second motor, and a switch from the positive of the first motor to the negative of the second).

One thing to avoid in your design is any possibility of connecting the B+ to ground through the relays, even if just for a moment during the switching. I think you'll have to make sure the controls and relays operate in a "break before make" so that the first two switches (used for high speed operation) are open before the one switch for low speed operation closes.

The other thought that occurs to me is that with this on-off-on sequence, there could be (maybe small) problems with inductive kicks when the PCM cycles between low and high speed.