Perhaps I should have captioned this "calling Randall G" given his expertise on this topic.
Here are the symptoms: The oil cooler fan on my 95 993(33,000 miles) does not operate on low speed automatically and only operates automatically at high speed intermittently. I have reviewed the archieves, Robin's superb site and followed generally the troubleshooting procedure. But, I am a moron on matters electical--although I do have a multimeter that I inherited from my electrical engineer father.Giving me a multimeter is like giving a monkey a watch. Back to the facts... The fan operates on low and high when jumpered. Terminals 2&5 have 12.22 volts which drops to 3.57 when the fan is jumpered on low. I measured no resistance across terminals 5&7, if I did it correctly. At one spot in the trouble shooting guide it says if the fan runs when jumpered, the ballast resistor should be ok; however, later it says an open circuit across terminals 5&7 indicates a failed resister.So, do I have I failed ballast resister? Should I give up and have the dealer sort it out? Will the hammer give a definitive diagnosis? If it is the ballast resister, has anyone done it themselves? It is supposed to be a PITA. Any guidance will be much appreciated.

 

Hi Don,

Randall G. here, enjoying my President's Day holiday at home!

Looks to me like everything you've done so far indicates your ballast resistor is A-Ok. A couple follow-ups:

>I measured no resistance across terminals 5&7, if I did it correctly.

This means you either had an open circuit (infinite resistance), or--more likely--had the multimeter set too high to measure the low resistance you are expecting. Some multimeters "auto-range" (set themselves automatically), others must be set for the expected range.

Anyway, since you got (approximately) the proper voltage drop when jumpered, and the fan runs when jumpered, it seems unlikely your resistor is failed. At worst, it could be failing intermittently.

>At one spot in the trouble shooting guide it says if the fan runs when jumpered, the ballast resistor should be ok.

Yes, this is correct. It means your resistor is intact, i.e., passing current to the motor.

>however, later it says an open circuit across terminals 5&7 indicates a failed resister.

This is also correct. It means your resistor is no longer intact (or "open"), and is not passing current to the motor.

>Will the hammer give a definitive diagnosis?

Yes, it should. In my case, I needed the hammer (equivalent) to verify it was my CCU that would not start the fan automatically.

> If it is the ballast resister, has anyone done it themselves?

Yes, Jai Choi has done this. If his summary is not already on Robin's site, it can be found at an updated version of the Oil Cooler Summary here:

<a href="http://members.rennlist.com/rgranaas/rgranaas.htm" target="_blank">Updated Oil Cooler Summary</a>

What I would recommend you trying next, if you haven't already, before handing the problem over to a pro:

-Does you A/C condenser fan come on with the AC, ignition on? If yes, then swap the equivalent AC condenser fan and oil cooler fan relays, and see if the cooler fan starts. You may just have a a bad relay.

-If this doesn't work, replace (or test, if you care to) the ~$16 oil cooler temperature sensor. If it is not operating properly, the CCU will never read the resistance value it's programmed to start the fan at.

Best of luck, and let me know how it goes.

 

Thanks for taking time out of your day off. This board is a wonderful resource. I sould have said earlier that I replaced the Temp sensor and this had no effect.My Ac works, so I'll swap out relays and see what that does. Curiously, my Ac fan will , on rare occasions, change speeds on its own and redirect the air flow. It is starting to sound as if my CCU is bad. I wonder if the Andial switch is the way to go-- I am not thrilled with the prospect of purchasing a new CCU.

 

All,

I just did some testing of the oil cooler fan and found that
the fan only comes on when terminals 3 & 5 (high
speed) are jumpered. The fan did not operate
when terminals 3 & 7 were jumpered. Also the was no resistance between terminals 3 & 7. This means
the low speed ballast/resistor is bad. Should I
also replace the A/C ballast too? Where is it
located? What about the thermostat on the oil line? Does anyone have a p/n?

TIA,

Tom

 

Tom .... yes, it looks to me like your oil cooler blower resistor has failed.

Does your A/C condenser fan start and run with the air conditioning, ignition on? If so, your resistor is fine. If not, you'll want to run the same tests on the slow-speed position that you ran on the oil cooler slow-speed position. That is, jumper test and resistance, but on the plug for Relay R14.

Don .... if you haven't already found out that your relay is bad, you're welcome to borrow my slow-speed jumper--I no longer need it, as I've since purchased a new $CCU$. The slow-speed jumper will verify positively that 1) your resistor is not failing intermittently, and 2) your relay is okay, as the jumper needs a good relay to function.

 

Randall, yes, I would be interested in your clever jumper. But, i have not yet swaped the relays and I want to recheck the resistance. Note that, in my original post, said that I found no resistance between 5&7; however Tom T measured across 3& 7. Did I measure the wrong terminals? I will check 3&7 and report back. if you don't mind.

 

Don,
What made you suspect that your oil cooler fan was not operating correctly? If it was increasing oil temperature gauge, excuse the dumb question, but other than that I would be unaware of the fan's operation. <img src="confused.gif" border="0">

 

Yup, I went for a fairly hard drive in about 50 F temps and noticed my oil temps up near appox. 230 F, and checked the fan near by the oil cooler and it was not on. So, i began to investigate further. The high speed fan came on when i let the car idle and got the temps up near 248, but the fan would only stay on for about 10 seconds. I still have not figured out the problem.

 

Don ... good catch!, you were correct in measuring the resistance across #5/#7.

Tom T. .... sorry, I didn't read your post close enough. You need to check resistance across #5/#7 to determine if your resistor is faulty. Measuring across #3/#7 does not check the resistor, and will give an open circuit.