Marshall M

Well, had the car on jack stands this weekend to install my new RSR mufflers and decided to check into a faulty Oil Cooler resistor. Did the checks on p-car.com and determined that the A/C fan worked fine and the oil cooler fan failed the low speed test. (BTW.....1995 993)

Pulled the nose off the car....(Decided to install a recently purchased K40 with the nose off....yea, I know...I also own a Valentine One and wouldn't trade it, but I love the lack of wires and suction cups on the windshield) and started in after the resistor. A few minutes later I had it in hand. I then decided to go after the A/C resistor and do a dual replacement with the updated Porsche parts.

Very surprised with what I found. I have posted a link to pics of the two resistors. You make the call which one was the "bad" unit and which one wsa the functioning unit.

<a href="http://boards.rennlist.com/upload/IMG_0961.JPG" target="_blank">http://boards.rennlist.com/upload/IMG_0961.JPG</a>

ApexL8

You gotta be kidding right?

KINGSRULE

Interesting picture. I think mine are gone also,
It seems the replacement resistors aren't different from the original ones. Have they infact been improved?
If not, are there better ones available to install?

TIA

STLPCA

Sorry, double post - brain fade.

STLPCA

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by GJ:
<strong>Interesting picture. I think mine are gone also,
It seems the replacement resistors aren't different from the original ones. Have they infact been improved?
If not, are there better ones available to install?
TIA</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">No apparent change in the resistor.
Porsche added a heat sink - a large metal washer with a locating slot that fits between the resistor & the mounting point to, presumably, dissipate the heat.
Only time will tell if that fixes the problem, although I have my doubts.
Since I expect to keep my car a long time, I relocated the resistors to a more convenient location inside the fender since I expect to have to replace them again ... and, maybe, again.

'95 993

I replaced my resistor '95 993 last weekend, a pain in the a*s! to get too, the most interesting point was that my resistor had corroded from underneath - between the resistor and the metal it was bolted to - this had led to its failure, so maybe the new shim between the resistor and the metal will help?

deltajetfixer

I'm going to do both the oil cooler and A/C fan resistors soon. Any thoughts as to putting dielectric grease between the new style metal plate, the resistor, and their respective mounting surfaces?

It seems to work well on IC's and power transistors...

MadMarkie

My resistor failed the low speed fan jumper test... so I soldered a bridge wire between the low and high speed terminals inside the relay (post with pictures a few weeks ago: "ballast resistor is toast"). Since it is so hot in AZ, I really like the idea of bypassing the low speed resistor circuit. I also plan on adding a manual switch soon, and perhaps an aux cooler, so I have more control.

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> my resistor had corroded from underneath - between the resistor and the metal it was bolted to </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica"> </font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> Any thoughts as to putting dielectric grease between the new style metal plate, the resistor, and their respective mounting surfaces?
</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Do most of the failures appear to be corrosion? The metallic disc included in the updated part might be designed to address a Galvanic potential problem, not heat dissipation. If anyone knows what material the ballast resistor and the mounting surface are, I can run it by the materials freaks at work tomorrow. I would bet they have some "magic goop" <img border="0" alt="[cherrsagai]" title="" src="graemlins/drink.gif" /> which would double as a heat transfer medium and a corrosion inhibitor.

deltajetfixer

[/QUOTE]Do most of the failures appear to be corrosion? The metallic disc included in the updated part might be designed to address a Galvanic potential problem, not heat dissipation. If anyone knows what material the ballast resistor and the mounting surface are, I can run it by the materials freaks at work tomorrow. I would bet they have some "magic goop" <img border="0" alt="[cherrsagai]" title="" src="graemlins/drink.gif" /> which would double as a heat transfer medium and a corrosion inhibitor.[/QB][/QUOTE]

The resistor itself appears to be a ceramic molding with an epoxy filler. I don't think galvanic corrosion is the issue.
Then again, at $40 a unit, maybe it's FERROceramic!!! <img border="0" alt="[hiha]" title="" src="graemlins/roflmao.gif" />

Edward

I had a ceramic chunk of the resistor literally hanging from a piece of the plastic shrouding under the car at my last track day. It was about a third of the ceramic insulator just hanging there on the AC side. So here's my question:

I know what the resistor does on the oil cooler side; what's its function on the AC side. My AC has been working perfectly fine for weeks now (and we've had some HOT days!) and I don't feel like "going in" until I have to. TIA

Edward

Randall G.

Hey Edward,

It basically does the same thing as the oil cooler fan ballast resistor. It drops the 12V supply to run the condenser fan at a slower speed. To run the condenser fan in fast-speed, the resistor is shunted by the relay.

Does your condenser fan come on with the A/C? It's supposed to, but won't run automatically if the resistor is bad. Without the condenser fan running, your A/C won't be as efficient. Especially when the car isn't moving. If system pressure gets high enough, the fan should eventually start in fast-speed.

<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

Edward

Randall, makes sense. Thanks! Yes, my fan comes on with the AC button. And since my AC gets very cool, I'll assume for the time being that it's doing ok, despite the missing chunk of insulator. I appreciate the answer.
<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

Edward

jebia

After reading this thread and the associated DYI link, I wanted to make sure I understand.

-When the AC is on, should the condensor fan always run (continuously), at least in low speed (or is it turned off and on by the CCU based on a temp, like the oil cooler fan)?

-When the AC is on and you either have high or low system pressure (low/high system pressure switch) the fan should run in high speed (I guess that assumes the terminal "Term 31" on the CCU is always at 12vdc when the AC is on)?

thanks in advance.