Alan

Does anyone have a link or details of the work someone did to change the operating sense of the water valve actuator - basically this reverses the actuation direction and therefore changes the default state (no vac) to closed rather than open. You do need to reverse the polarity of the signal from the head unit - but I'm contemplating this change next time I delve below the airbox... I like the idea of default cold for typical use in Phoenix.

Someone on rennlist definately did this and doicumented it with photos of how - I think they even just adpated the stock water valve bracket - but I'm not sure exactly how... This was a long time ago...

Alan

Gtaebr

Here Alan,

http://members.rennlist.com/v1uhoh/summer.htm


Joe

Alan

Thanks - but no not that exactly - this one maintained a fully functional valve but with a closed default position.

zip tying it closed is a possiblility - but I'd like to have heat on demand too - just only when I actually tell the system to make heat.

Right now in the summer the heater core gets full hot very quickly after parking when the valve opens - this makes cooling the car down fully take longer... trust me when its 115F outside and the whole car has been in the sun and the interior is at about 150F the last thing you want is a heater core full of 200F+ water - when it doesn't neet to be...

Tony did have some other interesting ideas there though (some of which could be accomplished electrically also...)

Alan

the flyin' scotsman

Alan.............at one point in time I suggested omitting all the vacuum controls and subing with small r/c type servos.

Having bigger fish to fry with the 928 haven't spent much eng. time to the potential.

The head unit in OEM config supplies the basic on/off signals.

ZEUS+

You could use a vacuum solenoid to control operation at will. One used for the flappy control or egr control on other vehicles will work.

Alan

Malcolm - I actually spent quite a bit of time looking at this and even investigated magnetically latching solenoids as possible solutions. The problem is that they need to be pretty big to achieve anything like the stroke & force that a vacuum actuator can deliver. Driving powerful enough solenoids continually is impactical for power reasons - hence magnetic latching - but they are expensive & big, hard to drive and the ones that are powerful enough switch very fast and that makes for very noisy flap changes (and likely risk of damage to the linkages etc).

I'm thinking the vacuum solution is actually a good choice (though they do need new diaphrams from time to time).

The only real option as on most current luxury models is a geared stepper motor style - but you need a whole new controller for these - and of course that allows for partial flap activations which is a nice control option - if the system is mechanically & electrically designed for it...

I investigated this with BMW activators - buts its just too much work to adapt it to what we have... for me anyway...

Alan

Alan

Zeus - But wait... it basically already IS a solenoid valve controlling a vacuum actuator... exact same thing as with the flappy?

It just needs to be reversed physically & electrically - Its not that hard to do - I could figure it out - but somone already showed how....

Alan

Hilton

I remember the post you're referring to - someone posted cad/cam diagrams of the modification.

I'll go check my subscriptions folder for HVAC.. its the kind of thing I'd have filed.

Hilton

https://rennlist.com/forums/928-foru...-hvac-mod.html

ZEUS+

The solenoids all share the same ground. The heater terminal 2/red wire is supply. I guess if you isolate the solenoid you could control it.

Alan

Yes the electrical swap is easy - just a relay to change the sense of the solenoid control.

Alan

Alan

Hilton - thanks - yes that was the one... excellent !!

Alan

docmirror

Man, I was thinking of a much simpler way. My plan was to just get one of those cheap manual choke cables and hide the handle in the glove box. During summer, connect the cable to the water valve arm, and in winter you could use the regular controls. Takes about 5 minutes to connect.

Alan

Doc - I don't consider that to be simpler - more like pain to have to keep swapping around (plus I don't want to have a choke control in my car ) Also note that without the water valve operational you actually have no temperature control - just max AC all the time - cooling amount controlled by the blower fan only... having to fiddle in the glove box sounds like a pain.

Temperature regulation in AC mode is still via the mixing flaps and hot water on demand. There are times here when AC is highly desireable but full AC is still too much.

I think that ideally this should have been the default stock behaviour for vehicles delivered to hot countries/areas - middle east, southern USA etc It would actually have been easy/cheap for Porsche to have enabled this (but yet one more specific difference to deal with).

Alan

docmirror

Potayto - potahto. I read the thread about changing the default state by changing the valve, then the vacuum actuator, and a relay, and more vacuum lines. Not that I have any trouble doing it, but the whole things get rather Rube-like.