Ballast resistor replacement

It is apparent that both of my ballast resistors are toast. I did the relay hack for a temporary fix, but I want permanent one. Two questions: Has anyone eliminated the ballast resistors? This would in effect make the fans run on high whenever they were on. Not sure this is a reasonable way to go. The fans are loud on high! Can the 944 resistors be used which are much cheaper? I don't know what the relative numbers are on each one respectively, but I suspect they are close to each other. The new ballast resistors are made of unobtainium, hence there ridiculous price. Ed, are you out there? You made a post about this about a while back... Thanks in advance! Best, TomF

HEY my ears are burning there is a jumper wire you can run inside the fuse panel so they in effect bypass the resistor - is that what you already did?

I've been thinking about this topic for quite a long time now. On the 993 forums, some people there have created their own resistor with a specific wattage dissipation to bypass the Porsche tax (nothing specific about resistors that should make them cost what they do). Essentially they found the stock resistance and made sure they bought a similar resistor with the appropriate wattage dissipation. If I remember the thread correctly, the individual even went so far as to decrease the resistance slightly (thereby providing higher voltage to the low speed fans to make them run a bit faster). I have been looking for the stock ballast resistor's resistance for some time now, with no success (and I'm newly learning electrical diagrams).

keep in mind these little buggers get bloody hot one the reason they might fail seems to be that they get super cooled with water splashing on them causing internal fracturing and thus failing Yes nothing special about them other than the shape/size/availability you could solder about anything in its place to reduce the voltage as long as it can be mounted safely, not come in contact with any surrounding parts and handle the power requirements My son just went through this on a computer monitor he bought that had a blown capacitor - the part was sourced out of Canada for $2 and not easy to find, but at the end of the day it fit the needs and solved the problem.

The stock ballast resistor's resistance is 0.5 Ohms. Because of size and price I used two of 1 Ohm/50W in parallel instead only one 0.5 Ohms/100W http://www.arcolresistors.com/resist...used-resistor/

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Sir, you've made my life much easier on this front. In this case, I would think a lower resistance might be nice for higher low-speed fan operation. Thanks again.

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Yep, I jumped the two relays and can get the high to run whenever the AC is on it is hot. If I eliminate the ballasts, then the DME will trigger the high at both temperatures, when the low should normally kick on and of course when the high should kick on. I think that I may bite the bullet and replace both fans as they come complete with ballast resistors for $175 each. Not too bad, I guess. Thanks to the others that suggested the resistance needed. I may get a 944 resistor and test its resistance just for my own curiosity. Does anyone have the part number? I only have pets and manuals for 911s... Thanks! Best, TomF

Porsche Parts Catalog(s): http://www.porsche.com/usa/accessori...artscatalogue/

I'm glad to help, you are welcome mmahon04 I made it two years ago and still working properly. My "piece of engineering" using the broken old ballast as base for supporting:

Very nice! Thanks for posting. What was the cost for the two? I still wonder what the resistance of the 944 unit is. I tried to find it on PET, but don't see it anywhere. Since it is completely sealed, it might last a bit longer. Cheers, TomF

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You are welcome, The cost was only 8 euros both.

Hi. I've got a similar problem with my 996. The ballast resistor pack is shot. A quick piece of checking reveals three wires, White, Green and Green/White. I've jumped the low speed relay and found that the Green/White wires goes to +12v. If I then remove this link and then link the high speed fan, the White goes to +12v. I assume that th Green goes to Earth (Chassis). If this is all correct, where do the resistors connect? Your DIY fix has red and black leads. Which leads on your DIY fix connect to the car wires? Any help would be appreciated. Other than this I'm going to have to change the complete fan assembly. Cheers

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My DIY ----- Car Black ---- Green Red ----- White Red ----- Green/White Both Red wires are connected together to the resistor.

Should I ever have the problem I will revise, modify, the circuit such that in low speed mode the fans are connected in series, ~6 volts each.

@Corven Thanks for the clarification. I'm going to give this a go as I don't really want the hassle of replacing the entire fan assembly. While I've got the front bumper off, I've decided to fit DRL's and some mesh to the air intakes to prevent leaves etc clogging up the rads. Just dug a ton of leaves and a dead bird out of there this weekend so well worth getting the bumper off. It really does only take about an hour to do the whole job and there are a few videos on Youtube showing how its done. You would have thought that Porsche would have fitted mesh to the intakes as standard!

I have just finished replacing my ballast resistor on the passenger side and I've done it a lot cheaper than using the genuine Porsche Ballast resistor. I'll do a step by step guide but if anyone wants any help, message me. I'll describe the passenger side but obviously if yours is drivers side then alter as required. Before you start, go to RS or similar and get a 0.5R 100W (RS code 188-071) resistor. This will cost you about �5 inc VAT. 1. Remove the wheel and support on a suitable axle stand. 2. Remove the wheel arch liner which will give you access to the ballast resistor wiring. 3. You should see the resistor on its clamp with the wiring coming from it. 4. I would disconnect the battery for safety at this point. 5. Cut the wiring as close to the old ballast resistor as possible. 6. Remove the old resistor and bin it. 7. Identify the three wires (green, white and green/white). Green = Low speed fan supply White = High speed fan supply Green/White = Output to fan motor 8. I suggest you get hold of a good soldering iron, you will need something quite powerful or use good quality crimp connectors and cover all joints with heatshrink, the stuff with adhesive in is the best choice. 9. Solder the White and Green/White wires to one side of the resistor and then cover with heatshrink. 10. Solder the Green wire to the OTHER end of the resistor and cover the joint with heatshrink. 11. Drill a couple of holes so you mount the new resistor where the old one used to be. Make sure its in the airflow of the fan. To test the new resistor. Reconnect the battery and make sure all fuses are good. First of all you need to know where the relays are. Look under the dash above the fusebox and you'll see a row of grey relays (each is marked with a large 53). Working front to back, they are : 1. Not important for this 2. Passenger side low speed 3. Passenger side high speed 4. Drivers side low speed 5. Drivers side high speed OK, choose which relay you need to pull, I would suggest high speed first of all. Once you've pulled the relay, make a short piece of wire ( 100mm) and crimp a blade type connector one each end. Use this to "jump" the relay. Connect from the top connection (vertical slot) to the bottom horizontal slot. The fan should run at full speed (you'll hear it). OK, now remove the link and replace the relay. Do the same again for the low speed and you should hear the fan run at a lower speed. Remove the link wire and replace all relays. Replace the wheel liner and roadwheel. Start the car and put the a/c on and set it to the lowest temperature, give it a few seconds and you should hear both front fans running at low speed. Hopefully the two pictures will work. One shows the new resistor in place and the other shows the front now I've fitted some mesh and DRL's. If anyone has any questions or needs a hand, message me. photo 3.jpg photo 4.jpg

Thanks for this write-up! I plan to try this this weekend.

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I did this fix last week. Both old resistors 7472D5B4-02D0-405E-9C4D-5937BE758A63_zpsab1tmkp8.jpg New ones 6392B2FA-4CB7-45C0-BBC6-D14C5EDD0D01_zpsjpvtjiab.jpg 0C3D25A0-7EF5-4354-A314-99258757E697_zpstohmaaon.jpg Car runs much cooler now. 20151130_123243_zpsowxeobfn.jpg Been tracking it for about a week now, and it runs 15-30 degrees cooler then it has since I bought it in Decenber of 2013.

I realize this is an old thread but I hope someone can help me. I recently replaced the driver's side ballast resistor in my 2001 996 cabriolet. I noticed that both driver and passenger side triangular shaped removable covers are missing from the underside of my car - this probably explains why one resistor went bad due to cold rain. I haven't been able to find a part number for the cover. Can anyone guide me to a resource with part numbers for under body parts? Thanks in advance!

If you've got the pdf version of the parts catalog, the underbody parts are in there, somewhere around page 240. If you need the pdf, it is here: http://www.porsche.com/all/media/pdf...96_KATALOG.pdf

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Thank you so much - this is perfect and I really appreciate your help!

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Sorry to bring up this old topic, but I have a question about the missing cover (if there ever was one). I recently had to replace one of my ballast resistors and would like to avoid having to do it again - especially if it's because it got super cooled from splashing rain. Is there supposed to be a louvered cover to protect the ballast resistor, or is it supposed to stay open to allow hot radiator air to flow through? If it is supposed to be covered, could anyone tell me the part number or take a photo to show me how it's supposed to look? Thank you!! missing cover?

It's supposed to be open like you said to let the hot air vent.

@Ahsai , thank you!

Nothing to add to the electrical info already in this thread but I did try a different mechanical solution to mounting the non OE resistors. The OEM resistors have exactly the same OD as 1/2" copper pipe which gave me an idea...a few pop rivets and some bent 3/4" pipe brackets later....

Thank you for the post. I'd seen others perform this, but they wired it wrong. Since the white and solid green wires come from the same cable loom and go to the factory resistor, they assume they should be soldered together on one end of the replacement resistor. This mis-wiring would result in both high and low speed operations going through the resistor and only getting low speed fan. Thank you for showing the right way

For the price, you could likely replace the resistor with a PWM controller. The it would be adjustable on both speeds.

I bought two of these resistors on Amazon for under $8 total (free prime shipping). If you can solder, this is a very cheap, easy repair that maintains the stock functionality. I have a new fan assembly with a new resistor that I will put in eventually, but this was too cheap not to try it out.

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I have diagnosed a resistor failure on my left fan, what I found on Amazon was this: Amazon Amazon Is this the one you used or at least is it equivalent? I am not at ease with electronic component equivalences... Thanks.

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Yes, 100 watt 0.5 ohm. That's what I used. Different brand, different color anodizing, same specs.

Both of my resistors had given up the ghost, so this post was very helpful to me. I did the soldering today on the new resistors, and tomorrow I'm going to my buddy's house to use his lift and install the resistors.996 owners don't need any additional heat in the cooling system! Thanks!