Whether AC is on or off, the fan only blows reliably on full (4) or when Max AC (big snowflake) is engaged. If I just want speed 2, for example, it may blow at 2 for awhile, then slow down or stop, then come back on. It has even blown when everything is off, fan set at zero!
Can anyone exorcise this demon???
TIA

 

Sorry to hear about your problem and I wish I had an answer for you - I just have an additional question.... I don't know if this is the same thing or not, but when I first start my car, put on the A/C, it keeps shutting off every few seconds for the first few minutes of use. Is this an A/C thing that's supposed to happen due to the humidity in the air? Some kind of balancing thing, or is it simply about to go out of service completely?

Steve

 

Hey jz,

Got a message that you tried to PM me, but that it bounced. Sorry about that, my PM folders are empty, I have nothing left to delete, but still get these messages. I've e-mailed John D., asking if he can help.

My guess is you have a problem with either your CCU, or your final stage regulator. The final stage regulator is what actually controls the fan speed, based on a signal from the CCU.

Any chance your interior fan isn't turning off when the key is removed? This would definitely suggest a bad final stage regulator.

As a long shot, I would still verify your rear blower operates correctly. A blown fuse will cause the interior fans to cut-out when heat is requested (and the rear blower doesn't start). Not quite the problem you're describing, but I would check it, all the same. Place the temperature control **** at "blue dot" (max cold), engine cold, turn on the ignition (warning lights on, but engine off, so you can hear better), then turn the temperature control **** to maximum. Within a few seconds, the rear blower (upper left side of engine) should turn on, trying to supply heated air to the cabin. If the blower doesn't run, verify its fuse (in the engine compartment fuse box) is good.

 

Randall, thanks for responding so quickly. Per your inst. , the rear blower is OK. Again with the ign. on and thermostat on blue dot, but all other buttons off and fan at zero, the fans blew like a blustery day in Chicago: fast, slow, medium, etc. changing constantly for about 15 seconds, when I turned ign. off.
It goes into the shop in the AM. I can't believe it didn't act like this when they checked the system last month.
Is the final stage regulator available seperately, or is it part of the CCU?
If they tell me I need a new CCU, I'm just going to drive with Max AC on the whole time, until it breaks completely.
Steve, sounds like you have a gremlin, too. I can't answer about humidity, I live in AZ Hope it doesn't get any worse for you.

 

Hey Jeff,

The final stage regulator is beneath the flimsy black plastic cover at the base of the windshield, inside the trunk. It looks like this:





The part is available separately, somewhere in the neighborhood of $125, give or take $20, as I recall.

Please let us know what the shop finds.

 

Yes, I looked it up on PET. PN 964 624 010 02 Price at my local dealer:
$ 347.62
Guess that's better than $1234.90 for the CCU.
I'll update ASAP. Thanks for the pics.

 

I have been in a car that has this erratic fan control as well. Is there an error code stored if the final stage regulator goes bad. Is there anyway to tell for sure if it is the final stage regulator or the CCU before replacing the cheapest part first?

 

Jeff,

Try shopping around on the net for better pricing. Sunset Porche has been great with their prices whenever I've inquired.

Good luck

 

>$ 347.62

I'm sorry Jeff, you're much closer than I was. I helped a friend diagnose his as failed about a year ago. Here's text from his e-mail, after getting the regulator replaced:

"Randall,
The part was about $250 and the labor the same. It was located in front of the firewall however I did not hang around to see exactly where. I ohmed out between pins 1 & 2 and between pins 6 & 7 expecting to fine a short between 1 & 2. Both were around 7.8 ohms. "

In his case, the fan continued to run with the key removed, and was draining his battery.

If you wind up needing a CCU, you can do much (much) better than dealer list price at a discount (mail order) Porsche dealer. For example, I only paid $760 for mine, same list price you were quoted. Alternatively, you can have yours repaired at (for example) Otto's of Venice. Around $350 or so, but don't quote me on that.

Good luck, and let us know how it goes.

 

CM993,

With my friend's car, we installed my spare CCU long enough to verify that the fan continued to run with the key removed. Which only left the final stage regulator as a possible cause.

 

Well my car is finally back in my garage after 5 nights. The tech. found that the condenser fan was only working on high, when triggered by high head pressure. So it was turning on and off alot, mostly off. He replaced the series resistor, located on the fan side of the condenser. They didn't write the part no. down, but he showed me the part. They charged $48.95 for it, and $222 for labor. (He also lowered the front spring perches 10mm, and topped off the power steering fluid, no addl. charge.)
It was a short ride home in about 105F heat, and the car was sitting in the sun when I picked it up, but it was cooling well, and the fan (dash outlets) now works at the lower speeds, with no interruptions.

Thanks again to everyone for their contributions to this thread.

 

Hey Jeff,

I think you have (or had) more than one thing going on here. The part your mechanic replaced was the ballast resistor for the A/C condenser fan. When the ballast resistor is bad, the A/C condenser fan won't run continuously in slow-speed with the A/C on like it should--the slow-speed circuit is open. As you described, it will cycle in fast-speed, fast-speed being activated by high-system pressure.

Now, we were talking of the condenser fan above. I can't think of a way for condenser fan operation to affect interior fan (the one you control from inside the car) speed. And, lots and lots of people (myself included) have had the condenser fan ballast resistor fail, the only real indication being cycling of the condenser fan. No impact on interior fan speed control. If nothing else, there's certainly no way for a failed ballast resistor to cause the interior fan to run with the key removed.

Are you sure your mechanic didn't fix something else besides the condenser fan ballast resistor?

Anyway, glad to hear your system is working correctly now.

 

Maybe you misunderstood. The interior fan did not run with the key removed. It ran with ign. on and fan speed set to zero. Turning the ign. off stopped the fan.
I also don't understand how a problem in the condenser can affect the interior fans. Today it seemed like it was blowing harder than expected on speed 1 for awhile, then slowing down to normal. Maybe I'm going batty from paying so much attention to it. Someday, probably, the CCU will need to be rebuilt. My income prevents me from shelling out $900+ for a new one. If dismantlers want an old one when they sell you a used one, they must be rebuilding them somehow. I may be ignorant, but I still think the rheostat within the CCU is wearing out. If I see another CCU on Ebay, I'll bid modestly. One went for $180 last month.
I'm getting the windows tinted next week, and if things stay as they are, I believe I'll make it thru the summer in comfort.

 

Hey Jeff,

Yup, this is confusing.

With regard to your interior fan, it never turns off completely with the ignition on--even when set to zero. Then again, it shouldn't change speed on its own, if that's what you've been experiencing.

There's also a small fan for the CCU's temperature sensor that can run for a short while after the ignition is turned off.

 

With regard to your interior fan, it never turns off completely with the ignition on--even when set to zero.
Thanks, Randall ! You're the first person to say that, after 2 visits to the shop. Feels good to be reassured. I feel the same way about the 993 as I did 27 years ago with my 914: this car has a wierd ventilation system