TomF

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

ivangene

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?

mmahon04

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).

ivangene

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.

Corven

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/

mmahon04

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.

TomF

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

mmahon04

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

Corven

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:

TomF

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

Corven

You are welcome,

The cost was only 8 euros both.

Porschey747

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

Corven

My DIY ----- Car

Black ---- Green

Red ----- White

Red ----- Green/White


Both Red wires are connected together to the resistor.

wwest

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.

Porschey747

@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!