Randall G.

Hi Mike,

This is an easy one. Jumpering between #3/#5 is fast-speed! In fast-speed, the resistor is shorted across, so your 34mv makes sense.

For slow-speed operation, you need to jumper from #3 (or #2--it's shorted to #3) to #7.

Good luck!

MikeF

Randall,

Right again! Anyway, I've reached a solution based on your advice. I was able to get 10ohm resistors only...so I used two of them in parallel to achieve 5ohms. Actually, with the wire and fuse, the effective resistance measured between 5.5 and 6.0. I connected it to the #6 leg of the relay and grounded to the nearest screw. Its funny...the first time I turned on the ignition, the fan started in low speed and went to high speed when I turned the ignition further (beyond accessory postition). I disconnected my jumper wire, double checked its resistance (~5.8r) reattached it and it is working perfectly...go figure. I just got back from a 60 mile "test" drive and the fan stays on low just as you described.

I could not be happier. Next project is to replace the AC ballast resistor later this week.

Thanks again Randall. You've saved me a bundle and I learned alot.

Happy Holidays,

Randall G.

Hi Mike,

>I was able to get 10ohm resistors only...so I used two of them in parallel to achieve 5ohms.

Very resourceful! You must have at least basic knowledge of electrical circuits, maybe more?

>the first time I turned on the ignition, the fan started in low speed and went to high speed when I turned the ignition further (beyond accessory postition)

Perhaps "left over" from when you had the temp. sensor disconnected? If you had waited awhile longer, I think the fan would have dropped to slow-speed.

Suppose you've figured out that the jumper is not as smart as the CCU, as it powers up the fan in slow-speed in the accessory position, besides the ignition position. The CCU will only power up the fan in the ignition position. So, if you just want to listen to the radio (for example, washing the car), you need to ensure the key is in the radio-only position. Interestingly, the radio-only position is not described in the owner's manual, but it certainly exists.

With the jumper installed, I think you'll find your oil temperature will never reach the 9:00 position. As soon as the thermostat opens (around the 8:00/188F position), the oil starts to cool.

Glad to hear everything has worked itself out. Look forward to hearing how the A/C condenser resistor replacement goes. Perhaps you can take some pics, and I'll add them to the summary?

Have a great Christmas!

964Cab

Oil Cooler Ballast Resistor:

I wonder if one took out the passenger side head light unit could one get to and replace the oil cooler ballast resistor ? I think the item sits atop the oil cooler fan. There are 4 nuts holding the fan to the oil cooler, I would estimate that the ballast resisor is sitting nearest to the top most forward of those 4 nuts. It feels like a fat donut with a plastic material around it.

MikeF

Patrick,

I thought about that too, but if you look inside with the mudguard removed, you'll see that the housing for the headlight (on a 964)is a solid enclosure with grommeted openings for wires...so, no access with headlight removed...would be nice. Also, you can see the top of the resistor and you are right...its as far forward as you can get. I doubt there's a reason for its difficult location...probably easier for assembly when the oil cooler is out of the car.

Randall, when I change out the A/C resistor I'll take a few pics and forward them to you. Hopefully I'll get to it later this week.

I can't take credit for any electonics knowledge whatsoever...the guy at Radioshack suggested the parallel setup. I just surmised that the wire and fuse were adding a bit more resistance. I secretly still wonder if either a relay or the temp sensor are bad. BTW, I measured the resistance of the sensor, cold, and it was high, I think around 20 ohms (r)...when it was warm, it measured much lower...around 4r...an indication that its working fine, but I still wonder.....

Best,

964Cab

Mike and randall:

I just learned that Porsche had updated the ballast resistors for both the oil cooler and the A/C condensor: It's noted in Porsche Tech Bulletin #1 of yr 2000 in October. I assume it is the same for both the 964 and 993 ?
BTW: On my 993 I can feel the oil coller ballast resistor. My 964 Cab ballast resistor is working on both the A/C and oil cooler (thankfully).

MikeF

Patrick,

Thanks! That makes sense...I'll pick up a new ballast resistor for the AC side tomorrow. Hopefully I can get at the thing without disassembling the front of my car.

Randall,

How long have you used you low speed jumper? More importantly, are you concerned for the longevity of your fan motor? I'm guessing that at low speed, the wear is nominal. Also, with the jumper in place, would your high speed fan still kick on if the temp were to reach 10 o'clock?

Thanks,

Randall G.

Hi Mike,

>How long have you used you low speed jumper?

About 3 months now ....

>More importantly, are you concerned for the longevity of your fan motor? I'm guessing that at low speed, the wear is nominal.

A little bit. But, in my case, the alternative was purchasing a $CCU$. And, as you suggest, it has to be less wear than running it continuously in fast-speed, as some owners are doing. Also, I know there are owners that run their A/C year-round, and I don't hear of their A/C condenser fans failing. Finally, the upside is reduced engine wear, as the oil will run cooler than the driven-by-emissions factory setpoint.

>Also, with the jumper in place, would your high speed fan still kick on if the temp were to reach 10 o'clock?

Sure will. As a matter of fact, if your mudguard is still off, try disconnecting the temp. sensor--the fan will kick into fast-speed.

Oh, and BTW, I'm sure your relay is okay, or else the jumper wouldn't be working. On the other hand, it is possible your temp. sensor is defective, although it's unlikely considering that the resistance is decreasing with rising temperature. You can either test it as described in the summary, or simply replace it at some $16.

Good luck on the resistor replacement!

Randall G.

And here is a photo of the notorious resistors, as provided by LarryN--owner of a '95 993 requiring replacement of both resistors.

Adrian

Dear Mike,
There are a couple of things you should be aware of. Firstly the 2nd stage blower is also the additional blower or the rear blower. The three fans you are talking about are "ALL" controlled by the airconditioning and heating control unit.
A blown fuse on the oil cooler fan means simply a short circuit. A failed sensor will not cause the fuse to blow. The fan has tried to run and drawn too much current.
The oil cooler system has two components which you may need to look at.
Firstly, is the oil thermostat opening and allowing oil to flow through the oil cooler.
Secondly the oil cooler sensor. This will activate the fan via the control unit at a specific temperature.
A common failure by mechanics using the Bosch Hammer is not to reset the DME fault codes before reading the control unit. You also need to reset these codes and go out again. You have no idea how long these fault codes have been recorded for.
Another point to understand. All the temp sensors are Negative Temp Coeff. Inotherwards when cold they have a high resistance (4K ohms) and as they heat up the reistance drops. Depending on the temp range it will be around 1K to 100 ohms.
Ciao,
Adrian
911C4

PS: Sorry for the delay but I have only been able to do this Bulletin board from home since yesterday.

MikeF

Adrian,

Please clarify...what is the "rear" blower that you refer to? Is this a fan in addition to the AC condenser fan and the oil cooler fan? If so, where is it and how can I determine if its working? The fan in the engine compartment works...just not sure if its running in multiple speeds. There's plenty of airflow in the cabin.

Also, an update...I replaced my oil cooler temp sensor and it solved the oil cooler fan problem. I have removed the jumper. When the temp guage reaches slightly above the 9 0'clock position, the low speed fan kicks on. Once the temp drops, it turns itself off. When I checked the old sending unit, it showed a resistance of 4 K-ohms when hot...about 20 K-ohms when cold. The new one drops far lower than this. So, I'm guessing the old one only worked partially, but not enough to turn on the fan.

Anyway, please clarify the "rear" fan question for me. I will likely replace the ballast resistor for the AC condensor later this afternoon.

Adrian

Dear Mike,
You are saying that the rear blower fan is working. I cannot find any other reference to a second stage blower other than this one. So I assume that your mechanic was telling you something that he interpreted.
The blown fuse on the oil cooler fan would not be caused by the sensor. The sensor output goes direct to the control unit. Maybe the fan was obstructed in some way. The blown fuse concerns me. However if it is now working after replacing the fuse then you cannot fault it.
The condenser fan ballast resistor is know to suffer damage from the battery vent. Near this resistor you will find a hose with an open end. Extend it and re-direct it.
Once you have corrected all these faults I would recommend that you have the fault codes reset. Drive around for a week or so and have them checked again.
The temp sensor has obviously failed and needed to be changed.
Please advise what the fault codes, if any after you fix all of this stuff up,
I will look again to see what the second stage blower is. Maybe this is referring to the high speed section of the oil cooler fan or the condenser fan.
Ciao,
Adrian.
911C4

PS: The rear blower fan should be running at low speed as soon as you select heat on the control ****. It will switch to high speed for a very short time based on the measured air temp in the pipes around the engine. There is a sensor in the pipe. This is known as "Additional Engine Cooling"

Randall G.

Mike--great news on the sensor! It makes sense that your fan wasn't starting if the old sensor's resistance was 4k ohms when hot. The resistance corresponding to the fan start point is 1k ohm (at 100C = 212F).

>I will look again to see what the second stage blower is. Maybe this is referring to the high speed section of the oil cooler fan or the condenser fan.

You're right Adrian--the wiring diagram for the CCU clearly refers to the fast-speed blower for the oil cooler fan as "stage 2." That's why I figured Mike's error code for "stage 2" was actually the oil cooler fan, as a blown fuse "takes out" both fan speeds (or stages).

MikeF

Thanks guys. Currently in the midst of replacing the AC resistor. The old one is definately baaaaad....literally 1/3 of the ceramic is broken away...maybe because of the battery overflow line. Unfortunately, the allen screw that held it in place was rusted badly...when I removed it, the head broke off and the rest of the stud is permanent! I will mount the new resistor in a different location and will forward pics to Randall for your document...I turned on the AC with the new resistor connected (hanging loosely) and the low speed AC fan stays on nice and steady...no more hi speed cycling....I love this stuff!

I have no idea why the fuse was blown as all fans work fine. It may have been blown for years!

Best,

Randall G.

Mike--it sure is nice when a plan works out and everything makes sense .

All this talk of restoring automatic fan operation must have gotten me fired up, because I've just ordered a new $CCU$ for my car. Not sure exactly why, as the slow-speed jumper works just fine. But, I've managed to find a source for a CCU at "only" $760--Hendricks Porsche. This is even cheaper than Sunset's relatively low price of $850 (list is close to $1300 ).

Question for Adrian, please .... The new CCU is the updated 964 part, but is a 993 part number with the 993's max. cooling button. Do you know if it will require any jumpers to make it fully functional in my '91? I seem to recall you only need the jumpers if you actually install a 993 unit, but I'm not certain.