Bill Gregory

I posted awhile back how to use a cup bypass pipe, with associated electronics, to bypass the rear engine-mounted fan and fool the HVAC system that the fan was still there. I've heard from two people who made the modification, where the HVAC behaved as if the fan wasn't there, ie, looking for heat, turn the fan on, it works for a few seconds then dies. The common thread in the 2 instances I know about is that they are 1990 models. Porsche upgraded the HVAC control in 1991, which may have something to do with the problems the two 1990 owners experienced. Although a limited sample, since they were both 1990 models and Porsche updated the HVAC control in 1991, I wanted to let you know about this, in case anyone else with a '90 was scratching their heads over the mod not working as they expected.

If anyone has installed this on a 1990 964, and it's working fine, I'd appreciate it if you'd let me know.

Adrian

Dear Bill,
Not only did they upgrade the controller but 1989 and 1990 models also needed a modifcation to the wiring to be carried out. A jumper wire has to be made and installed between pins 1 and 19 of plug G. This will solve the problem of the front fans but you will need the new controller as well because the old one will play up with this modification installed.
The other thing is you could advise people to leave the temp control in the blue dot position at all times.
Ciao,
Adrian
911C4

schubee

Thanks for the update. I purchased a bypass pipe but haven't had the time to install it. Since I do have a '90, I'll install the jumper wire as Adrian noted. However, since I'm not an electrician, I'm sceptical on building the box connector with all the transitors. Do you guys know anyone who would build me one for a fair price? I just want to make sure this is installed correctly.

Thanks,

JW in Texas

Bill,
You've been mind reading again <img border="0" title="" alt="[Eek!]" src="eek.gif" /> I did the resistor mod to my '90 today & guess what, it doesn't work. Oh well, since I live in Texas, I'm not going to get too worked up about it. Now if it was my A/C, that would be a problem!

Bill Gregory

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"><strong>I'm sceptical on building the box connector with all the transitors.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">John,

Don't make it more complicated than it is. In the box I put together, there are only two added resistors, and one resistor that's already in the engine compartment. And for the two added resistors, only one is soldered to wires. The small one, next to the curly wire resistor, was soldered to lugs then plugged into the existing socket. I know another person who just pushed the resistor leads into the same socket. When I was putting it together, one or two people in the know suggesed I just wrap the resistors in tape and put them on the side of the engine compartment, however, I chose to mount them in a Radio Shack plastic box (given that one resistor generates heat, tape may not be the best solution). You may want to find someone locally who can use a soldering iron to help.

David Green

Adrian,

You mention plug G. I don't have a workshop manual, so where can this be found ?

Additionally, the controller you refer to is that heater control panel next to the radio. I am assuming it is, but could you clarify.

David

Euromagination

Wow. Talk about a blast from the past. I think I was still in high school when this thread was first made. LOL, jk.

Question to Bill (or anyone else who knows), if you see this... I just installed my blower bypass and I am experiencing these same problems that I think you described above. My 964 is a 1990 as well, and I hooked up the resistors as you did after being pointed in that direction by a fellow Rennlister (thnx garrett)...

When I first start my car, all kinds of air blows into the cabin so i know the other 2 front blowers that are still hooked up have plenty of power to do the job and move the air i want, but the problem is that they're just not doing it? It seems nothing is "telling" them to turn on??? Lack of electronic communication?

It confuses me? I don't see how they have all that power at first, then stay dormant for the rest of the time no matter where i move the *****. I was under the impression that after the electronics were hooked-up the front two blowers would start to "listen" again, but that's not the case so far. ???

(Once more in different words for clarity)... when I turn the car on the front blowers work very well and push a bunch of air until a few seconds later when the car sort of "notices" that the rear blower isn't hooked up (or something). At that point the front blowers shut down--leaving me with only the moving air from driving at speed to push the heat out into the car's cabin. It still gets hot after a little while so it's not the end of the world, but I'd like to find out how I could trick the front two blowers into working as well as I know they can and "listening" to the "0-1-2-3-4" fan speed ****.

One main question I still have is what does Adrian mean when he says "...Not only did they upgrade the controller but 1989 and 1990 models also needed a modifcation to the wiring to be carried out. A jumper wire has to be made and installed between pins 1 and 19 of plug G. This will solve the problem of the front fans but you will need the new controller as well because the old one will play up with this modification installed."

Does this mean that even after the jumper wire is made on a 1990, that I will still need to swap controllers out? A controller being the front panel, or...?

Is there any other further information on this that you or anyone else has learned?


Thanks!
Harry

BLK964

I bought a bypass a long time ago, before I read that it would require replacing the CCU. I haven't attempted to fit it. So, if someone has an alternative for us 89-90 owners, I'd like to hear it, as well.

Thanks,
Jason

Euromagination

shameless bump

Shahrams

Hi Bill, here you can find an article how to bypass the blower:
http://www.porsche964.co.uk/