Carrera footwell blowers - electrical questions

[ischmitz]

So I am looking at installing the Carrera footwell blowers to beef up the heating a little bit in my Targa. I read through the Porsche Workshop manual to better understand how they are controlled. Somehow what I found doesn't make sense:

In section 801-6 Heater is a paragraph on the "footwell blower series resistor" and it shows the huge green ceramic resistor pack. So my assumption is the resistor pack is used to produce a couple of different speeds by putting it in series with the footwell blower motors.

However, reviewing the electrical diagrams in section 970-45 onwards shows that resistor pack NOT to be in series with the footwell blower motors at all. The footwell blower motors receive straight GND from G116 on one side. The other side of the motors goes to Terminal 87 of the "Additional fan relay" which is supplied by Fuse 2 (25 Amps) on Terminal 30 from the battery.

My questions are:

1. Does the original setup in the 89 Carrera use one speed for the footwell motors or multiple speeds?

2. If there is more than one speed setting what am I missing? The resistor pack seems to be connected to the blower control unit and so is the engine compartment blower motor.

3. What is the green resistor pack used for? Is it to control the engine compartment blower fan speed?

Thanks,
Ingo

[Rot 911]

The footwell blowers only have one speed. The resistor was used to engage the footwell blowers only when the engine compartment blower came on. For you it would be easier just to install a power switch on the dash.

[ischmitz]

Ok, thanks for the info. I still don't quite see what the large resistor is doing in the stock install. From its size it sure can sink some power. Anyhow, I will probably use it to rig up a variable-speed option like shown here: How to Install footwell blowers in pre -84 911's

[mjshira]

Ingo

I did this install on Scruffy 1, works awesome and I use them for just one speed because I didn't think I'd make much use of the variable speed you can accomplish with the resistor. I didn't document my install or wiring but the set up should be pretty simple. I've got a basic toggle switch with two positions, on and off.

Let me know if you get stuck, I can call you.

[Mysterytrain]

I beg to differ. The footwells have 3 speeds. The heater console between the seats provides the speed control. On the manual heat versions the numbers go from zero to 3 with 3 being high speed. On the autoheat versions the numbering goes from zero to 9 and defrost which is high speed. Even with the zero thru nine numbering there are only 3 fan speeds. The speed resistor is located in the trunk behind the glove box. It provides the voltage drop for the slow and medium speeds. The additional fan relay provides the high speed by applying 12 volts directly to the footwell blowers. The relay is used as a high amperage switch because the switches in the console are too wimpy to handle the current.
I installed footwells on my 78. I have SSI's and no rear blower. I have more heat then I ever had. Its really a great little project. Here is the link:
How to Install footwell blowers in pre -84 911's

[mjshira]

you are right, no need to beg! ;-)

I just configured mine to run on high.

[Dennis Kalma]

I've always wondered why they just didn't run the wiring so that low speed would run both fans in series electrically and high speed would run them in parallel electrically. Haven't tried it, I admit, but I suspect that the two motors in series would run much slower and save the hassle of a resistor pack, albeit at the expense of a bit of extra wiring....

Dennis

[ischmitz]

Mark - since I happen to have the green resistor I might as well put it to use. How are things?

Ron, I read your thread - great writeup. I haven't crawled into my car yet to see how the stock setup looks. I like your idea of the stealth install. I was wondering if you could tell me which hoses I need in addition to the blower motors to do the install. I assume #10, #12 at least. How about the Y-pieces #13 and #18. Are they on my car (1974) or would I need those parts as well? Can I cut some of the existing hoses to do the install or do I have to go on an extended parts hunt?

Cheers,
Ingo

[ischmitz]

Originally Posted by Dennis Kalma

I've always wondered why they just didn't run the wiring so that low speed would run both fans in series electrically and high speed would run them in parallel electrically. Haven't tried it, I admit, but I suspect that the two motors in series would run much slower and save the hassle of a resistor pack, albeit at the expense of a bit of extra wiring....

Dennis

Maybe if the motors are not exactly the same maybe their speed would be very different since the resistance/speed relation is probably not linear. Just a guess.....

[Rot 911]

Ron is correct, I went brain dead. You would have thought as much time all of us spent figuring out how to make them work without the engine blower I would have remembered that!

[DByers]

socks

[ischmitz]

Originally Posted by DByers

socks

Well, for the time being wearing socks literally is a PITA - I fractured the left one last Wednesday....