A/C recirculation flap actuator function
 

1990 GT: with the air con on, the recirculation flap closes about 80%. Thinking that the actuator is NOT variable, but will only be fully open or fully closed. Is it possible the diaphragm can have a small leak and not hold a fully closed position? I am able to hold the flap closed manually, so there is no debris blocking the flap. can someone confirm the workings of this actuator, thanks.

The actuator could be leaking slightly but you may also have a weak vacuum caused by either a leak in the reservoir or other actuators that does not fully drive the actuator.

Best thing is to isolate the actuator and do a vacuum test on it to see if it is holding vacuum. If it holds then somewhere else in the system is weak.

It is a bit fiddly to get to the vacuum distribution manifold under the centre console but quite easy when you get used to it.

In what mode does the recirc flap close on a 1990, "Max AC" only? If that's how it's set, then yes, should close completely unless there's a loss of vacuum somewhere or blockage of some kind.

IIRC the recirc flap should be open (i.e. recirculating air supply) any time the temp setting motor is driven to 90% cooling or more based on the cabin temp. Once the setting motor drops below 90% cooling the recirc flap should close (i.e. fresh air supply.)

Mike

Hello Tom,
Yes the flap is closed on Max AC. Will isolate that valve and observe its operation.


On another note, how efficient is the Porsche AC system? took a 2 hour drive with ambient temp of 97 and while I was never uncomfortable, the AC fan was on high the entire trip. i would have preferred that after a while i would need to drop the fan speed down?? comments????

Hi Mike
Thanks for your reply; the flap should be COMPLETELY closed in that mode?

The system itself works very well. The limiting factor is the condenser. It just can't exchange heat fast enough to get the AC freezing cold.

Greg Brown has an upgrade that adds another condenser to the S4+ cars and Griffiths has a kit that exchanges the serpentine style condenser for a modern parallel flow unit.

I also find the fan itself to be a bit weak...that combined with the narrow ducting and vents, it just doesn't push that much air.

I believe there is an upgraded fan available, but I have no experience with it.

To the OP, yes, the flap should be either completely open or completely closed...it shouldn't be partially open.

I am not a fan of the 928 AC for a variety of reasons ... for one, I had a '94 968 before my GTS that would freeze me out. 100 degree days, rarely needed the second fan setting!

How could Porsche get that kind of cooling with one model when the 928 requires max/recirc + highest fan setting to get any cooling to speak of ?

Tom
that's not good to hear.....I hope I can find a way to get some better cooling!


UPDATE: I think my blue/black one way valve is the culprit. Bypassing the valve allowed all the HVAC functions to work properly.

If you do not get the recirc flap closed the a/c system will struggle as it tries in vain to cool ambient air.

The 928 a/c system is not brilliant because it is limited by surface area on a condenser that is comparatively old tech that sits in front of a very low profile and could be bigger where it not for the tranny cooler. That being said if the system is working correctly then at 100F it should still cool nicely once the heat soak is dissipated.

Performance is also afffected by relative humidity given the water vapour has to be cooled as well as the air. Thus if you live in a very humid environment the system wil struggle relatively speaking.

Heat film also helps system performance. The 928 has a lot of glass compared to most sports models and does not help either. When my system is optimal it works reasonably well at 45C even with R134a but that is when cruising- not in heavy traffic. I seem to remember Sean recommends an auxiliary pusher fan in front of the condenser to help things out in "slow" conditions. Additional condenser surface area is also most welcome.