BS911

LOL!!

Well, no. Actually, it started with the heater problems which then revealed the underlying circulation problem - which related to my ac problems I have in the summer. Maybe it is time to yank that ccu, heater blower, compressor, and a boat load of vacuum line out of there and drop a few pounds.

BS911

Randall IS the man on this stuff... and I can't say enough how much I appreciate your.

So... taking what I've learned so far and combining it with some searches through the archives, I think I am understanding that there is a vacuum and servo controlled portion of the fresh vs circulated air. It sounds like perhaps my fresh cool air supply servo is stuck closed or not getting signal from the ccu. (Remembering ataman's open circuit on g18.) Will try and check on that today.

Also, speaking of the temperature sensor... I think that is my problem #4 as I do get a "dwindling" supply of heat sometimes where I have to keep turning the **** up and up. Additionally, does it have a role in shutting off the ac compressor on an overly hot scenario? Wondering if it leads to my ac problems in the summer.

BS911

ooh... excellent. Might be another place to look for why the first 20 minutes or so after sitting in 100 degree sun all day, my ac compressor won't kick on. After some airflow "cools things down" - bingo. The compressor kicks in and nice cold air begins. Thanks for the confirmation!

Randall G.

Thanks for the kind words, guys.

Brian...there's a great HVAC servo article, written by Roly Baldwin, on John Mile's 964 web-site:

http://www.porsche964.co.uk/technical/servos.htm

The two main differences between the 964 & 993:

-The 993 uses vacuum control for the cabin air intake.
-The 993's mixing chamber servo motors/flaps are in the cabin footwells.

In your car, you want to take off the flimsy black cover at the base of the windshield, in the trunk, and make sure the fresh air intake servo is operating when you push/release the recirc button. Or, similarly, when you turn the A/C on and off.

Actually, before you even go this far, you can simply listen/feel for changes in air-flow at the fresh air intake, as you turn the recirc/A-C on and off. Having the interior fan at a higher speed will make changes easier to detect.

Good luck!

Randall G.

Hijacking the thread, just for awhile...

Mike, a few more tips/ideas:

-With the engine fully warmed, turn on the ignition (warning lights on but engine off), turn the temperature control **** all the way to maximum hot (or close to that). With the ignition on, the rear blower will either (should!) start to provide warm air to the cabin. Or, it will run for its other function = engine cooling.

-You can try the above with the engine running, but it's more difficult to hear the fan running. You may be able to feel vibration on the blower casing when it's running.

-Check for 12V at plugs #2, 3 & 8 in the relay plug (relay removed).

-Check resistance between plugs #5 and #7. Should be around 350 ohms if the ballast resistor is good, maybe a little higher.

-If you find 12V, try swapping the relay with either the A/C condenser or oil cooler--they're the same relay. If the A/C condenser relay is good--and the blower's ballast resistor is good--the A/C condenser fan will turn on automatically with the A/C (verifies the relay's slow-speed contact is good).

-Finally, you can jumper #2 or #3 to #7 (with a decent gauge jumper wire) to test slow-speed, #2/#3 to #5 to test fast-speed.

Hope this helps....

nile13

Randall, this is _exactly_ the info I needed.
Preliminary findings - the fan doesn't run with the engine warm as you've described (but I'm not sure it's fully warm). The heater blower relay is very different from both condenser (green) and oil cooler (black) relays. Did I misunderstand about swapping the relays?
It's dark out there now, but I will try with a voltmeter tomorrow or Monday and will report the results. It seems that jumping 12V to #5 and #7 should test the fan in a pretty obvious fashion. BTW, how does the fan come out?
Thanks!!

BS911

Ok... My first problem confirmed. The servo that opens/closes the fresh air intake flap under the windshield - kaput. Took the thing out, opened it up and did sime "fiddling" with it to see if the otherwise fired looking circuit board could be jump-started and I was able to get it to move about twice, but then it gave up again. So part #1 is up for order.

So I know that nothing about this sysem can be simplified but how's this for a diagnostic:

On blue dot, no recirc selected, no ac selected, just basic fresh cool air - if there is no air flow despite the front blowers operating, the electronic servo under the windshield is not opening - and stuck in the closed position.

On to problem #2 - that evasive vacuum leak that exposed problem #1.

Where might I find that outside temp sensor?

Randall G.

Good news, Brian. At least you've found your problem, a relatively straightforward fix.

>Did I misunderstand about swapping the relays?

I think you did. The condenser and oil cooler fan relays are in the luggage compartment fuse box. If you're looking at a green relay in the engine compartment fuse box, it's for the A/C compressor.

>It seems that jumping 12V to #5 and #7 should test the fan in a pretty obvious fashion.

Sure is. If it doesn't run when you jumper to #7, but does when you jumper to #5, almost guaranteed your ballast resistor is bad.

>BTW, how does the fan come out?

Here's a DIY on replacing the rear blower on a 964. Pretty similar for a 993. Though, I don't think you're ready to pull the fan just yet--you don't know for sure it's bad.

http://www.pelicanparts.com/techarti...ower_motor.htm

nile13

Randall, as usual, was right!

My lack of high speeds on heater fan was due to bad rear blower relay in the engine compartment. Replacing it with a good relay gave me higher and highest airflow on positions 3 and 4 of the blower controller. I'm still not sure that positions 1 and 2 give different flow, but that's a very secondary issue. As I had problems with windshield fogging several times before, I am very greatful for this solution.
The relay is a VW-Audi part, 811 951 253 (it also says 89 82 99 on it). I need to cross-reference that to Porsche # or better yet stop by at a VW dealer that is 5 minutes away and get a replacement. I will also try to re-solder the contacts on the bad relay today just to see if that wakes it up, more a curiosity than anything else.

So, once again, my thanks to Randall.G, a true guru of HVAC! :-)

Now I need to figure out why my cruise cotrol is not working (fuse is OK) and what these extra connectors are doing in my engine bay (could they be the unused connectors left over after the harness recall was done?)