Malmsey

I have searched and read the numerous posts regarding faulty servo motors, and I have found them very useful, but I have not seen an answer to the question of air flow.

I have a feeling my center vents aren't blowing enough air, but I'm not quite sure if they just are weak or there is something wrong. After removing the plastic shield in the luggage compartment, I noticed that the 2nd servo (driver's side) is dead ( OK, though because it is stuck in the cold position) and this was the only malfunction I could determine. Although it seems that even though the 2nd servo on the passenger side is operating the air is never hot ( driver or passenger) when you turn the temperature ****. The servo moves, but the air stays cold or maybe a little warmer. Of course when I remove the armature from the broken servo and move it manually you can feel the hot air.

Now my question is mainly to the air flow not the temperature. When I turn the blower to 4 it makes a sound that would imply a great deal more air flow than I am getting from my center vents. When I turn it to hot this air flow increases (I guess this is due to the blower from the back?). Overall though it is weak. You can't feel it sitting in the driver's seat. (You can feel the air coming out if you put your hands in front of it)

Now when I was messing around with the servo's I noticed that the passenger side of the luggage compartment was getting warm with the heater on. The passenger side servo is operating but no hot air is blowing in the cabin. I was wondering if the center vents are just weak in general or if there is some other problem like a fan is misalligned or something. What should I do next?

Overall this seems user-serviceable and that I can fix it without the aid of a mechanic. Does anyone have any suggestions?

Thanks.

Adrian

Dear Malmsey,
The heating/airconditioning air distribution system on the 964 is quite complicated. The centre vents are not controlled in any way by the servo valve you mentioned.
There are 5 servo valves.
LH Mixing chamber
RH Mixing Chamber
Defrost
Fresh Air
Footwell
There are three fans
LH Blower (speed controlled)
RH Blower (defrost fan)
Rear Blower (heater fan)
The LH blower fan runs all the time even with 0 selected on speed control. RH blower only runs when defrost button is selected.
Rear blower runs at low speed whenever the temp selector is turned out of blue dot position.
If you are not getting heast in the front your heater plumbing has come adrift in the engine compartment. Somebody else had this problem not so long ago. You have to fix this first. Once you have fixed up your plumbing you can then start troubleshooting the rest.
I suggest actually you have more than one servo valve failed. However one step at a time when troubleshooting.
The centre vents have no weakness. The airflow from them is determined by blower speed and forward speed.
Ciao,
Adrian
911C4

PS: Your post was a little confusing I hope I managed to read it correctly. I am assuming you still have little or no hot air through your vents. What about the side vents, anything through them. A stuck defrost valve can cause restricted airflow through the centre vents. Check airflow at windshield.

Malmsey

Thanks for the reply. I get heat in the front if I disconnect the arm from the LH (driver side? This is the one that is right next to the metal and insulated lines) servo and manually pull it out. The RH servo operates, but I don't seem to get heat when it moves. It rotates when I move the temperature control. Although heat builds up in the right hand side of the luggage compartment. (where the fan is.) I know the footwell servo is working as it rotates about 1/4 with one vent open and 1/4 more with both vents open. The servo on the extreme right (driver's side) moves as well. What is the center servo? I do get flow through the side vents.


Thanks

Adrian

Dear Malmsey,
I suggest that despite the fact that the servo look like they are moving they are not. Moving the flapper valve that is. This means the mixing chambers are shut off or in full cold position. This will cause a build up of heat in the plumbing as I feel you are experiencing. The centre servo valve I think is defrost but only off the top off my head I cannot remember 100%. So to fix this problem you have to replace the bad servo motors. It is not uncommon for both to fail by the way. If you do not fix them and leave the heating on, you may end up with a little fright when the rear blower fan cranks up to full speed whilst you are driving or at low speed as you walk away from the 964, as it dumps the overheated air to atmosphere,
Ciao,
Adrian
911C4

boxsey911

I've dragged this old thread up via the search engine. It gives me an idea of where to start but doesn't answer my problem so any help would be greatly appreciated.

When I direct the air flow solely to the face vents and turn the fan control up, I get no air flow out of the doorside left vent or middle left vent. The middle right vent and doorside right vent are fine. If I direct air flow to the screen or the footwell vents, these appear to be find too.

Have I got a problem with a fan blower, a flap, the plumbing or a servo? And are all these items to be found under the cover under the front hood?

OUR9II

Steve,

Have you found Roly's site yet?

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

Lots of good stuff. The reference links are broken but you may still be able to navigate to them through another Renlist search.

boxsey911

Thanks Mike. Yes I use http://www.porsche964.co.uk/ a lot to find stuff abour our beloved (and frustrating) motors

It turned out to be an easy mystery to solve. The left vent's thumb wheel is broken, the flap was stuck closed and it was in the wrong way round! So that's another item added to my wanted list.