Carrera - Removing Engine Compartment Heater Blower
 

I thought I'd share this:

If you ever wanted to remove/disconnect the Heater Blower in the engine compartment of a Carrera you will quickly learn that the foot well heater blowers inside the car no longer work.

This is because by design Porsche decided that if the rear heater blower is not connected or the motor blows out they did not want the heat system to run.

If you ever backdate your exhaust to SSIs (as I have done) you may wish to eliminate the rear heater blower and go with a setup like this. (not my carrera, just a picture I have of a CIS car, but you get the idea)

http://forums.pelicanparts.com/uploa...1200926432.jpg

Very clean engine compartment which uses the pre 1975 style heat system in the engine bay.

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Now for the point of this post: How do you get the front footwell blowers to work without the rear blower connected/removed?

I found nice solution that requires NO wiring changes, it requires a easy modification to the heat controll relay that is in the engine bay see pic:

http://forums.pelicanparts.com/uploa...1200926774.jpg

Remove this relay from the car, next we will open the relay but before we do mark it as follows so you know how to put it back together:

http://forums.pelicanparts.com/uploa...1200926957.jpg

Then, with a screwdriver peal back the edges of the tin (Carefully!) till you can get the relay apart, it will look like this:

http://forums.pelicanparts.com/uploa...1200927051.jpg

Once apart notice the Reed Switch in the picture below:

http://forums.pelicanparts.com/uploa...1200928030.jpg

OK, now for the details on the reed switch: notice the coil (3 winds of thick wire) around the glass tube. The coil and the glass tube are the reed switch. The way this works is that the coil is what delivers the 12 volts and the current to the rear blower, this means that if the rear blower is disconnected then we have NO current through the 3 winds in the coil. Only if we have current being delivered to the rear blower will the reed switch (glass tube) close. Once the reed switch makes contact (closes) then the small relay at the top of the picture will be energized. The large relay at the bottom is the relay that feeds the coil and the rear blower, this relay energizes when you pull up on the 2 heat levers between the seats. Once the large relay starts the rear blower the reed switch closes and then the small relay at the top of the picture energizes and delivers 12V to the footwell blowers.

So it is fairly easy to just short out the reed switch, doing this will just activate the small relay (foot well relay) the moment the large relay (rear blower relay) is energized. What we want to do is activate the footwell blower relay without having any current through the reed swich coils.

To short out the reed switch all that needs to be done is solder a small piece of wire across the reed switch on the back of the board like this:

http://forums.pelicanparts.com/uploa...1200927787.jpg

It's that easy! just re-assemble the controller relay and install it back in the car, you are done!

Here are a few more pictures I have as well as schematic of the Heat Controller Relay (hard to find)

Heat Controller Schematic:
http://forums.pelicanparts.com/uploa...1200928234.jpg

Pic of the controller:
http://forums.pelicanparts.com/uploa...1200928257.jpg

Overall heat system schematic:
http://forums.pelicanparts.com/uploa...1200929232.jpg

That interesting! I never knew why my foot blowers didn't work without the rear working. I always thought it was just that Damn German wiring thing again..Thanks

I think the Porsche Engineers where concerned that if the rear blower was not running then the front foot-well blowers would be sucking air through the heat exchangers (negitive pressure, vacuum) and this could result in CO in the cabin. I speculate here, but I think they wanted to keep the exchangers with positive air pressure at all times.

No matter the reason the bottom line is that the front foot well blowers will not run without the rear blower running.

Hope this helps.

Nice write up. I backdated my heat a while ago so this would be a good thing.

interesting. i have an 85 and my blower motor bearings busted. I removed the motor and put some ducktape over the hole where the motor attached to the housing. now, when i turn on the heat i get good heat when the car is moving above 10MPH. :) on the highway? shoot...it's like i have a blower motor running back there!!! the ONLY problem is now the defrost motor in the front won't turn on...you know the little knob by the heater pulls? Any ideas? So I end up running the "fresh" air motor to at least blow cold air over the windshield.

then again, i'm in texas and it gets 32 degrees at the COLDEST.

Great post!

Where are you in RI?

I'm in Portsmouth, RI - send me a PM

Hey Sal..we covered this a few years ago!! ;)
http://forums.pelicanparts.com/showthread.php?t=258473&highlight=engine+compartme nt+controllers

How are the dashlights doing..its next on my list.

Yes Ron, much thanks to you on this work as well. It was just that I never really had to remove the rear blower till the other day So I took what you help me learn a while back and actually modified the Relay and took some pictures and wrote it up in simple terms for folks to understand the mod.

The Dash lights are great, I love the brighter dash.

Was nice hearing from you, hope you and your car are well.

Sal, what can I say? This worked like a charm.
Thanks for writing this up with instructions that even the electrically challenged like me can understand.

I don't need my blowers at all, but you guys have provided some great info for the rest of us...thanks Sal & Ron!

Graham,

Glad to hear this worked for you. We owe Ron (MysteryTrain) thanks as well, he helped me understand the control relay and most importantly he helped obtain the schematic for that relay.

This solution is far easier and cleaner than putting load resistors on the harness.

I completed the backdate on my 87. Thanks for all the info on this topic. I left the A\C compressor\system alone and just removed the engine blower motor and left-side duct work. I opened the heater relay and jumpered the reed switch (just like the pic above), but when I start the car and pull the red heater levers, the foot-well blowers do not turn on. They only turn on when I rotate the heater knob between the seats. Is this how this mod is supposed to work? Or should the foot-well blowers turn on when I lift the heater levers, just like it did in it's stock setup? Thanks in advance.

The jumper simulates a 'blower running' condition, however I believe you need to turn the rotary switch in order to energize the footwell blower relay. At least that's how my backdate works.

Thanks for the info Trog. I could not not recall any info in regards to "how" the blowers were supposed to activate after this mod was completed. If this is how they are supposed to work, that's fine, but I wanted to make sure that I did not goof it up.

Just a note,

The Engine Heater Blower also works as an Automatic Cooler for our Carrera's. At a certain temperature (180F as I recall) the blower kicks in and attemps to cool down the engine to proper levels.

So you SouthWest Guys should consider repairing the Engine Blower Motor.

This is normal, the heat levers activate the relay only. The foot blowers will only run when the rotary switch is turned.

Thanks for confirming Sal and for sharing this info! Ron too!

Ran into a snag this morning...

Got in the car this morning, lifted the heater levers and turned the center knob. The footwell blowers started up. All was fine, then I smelt an electrical smell, and turned the knob off, but the right footwell fan kept spinning (low speed) and the left one does not appear to be working at all. I turned the car off and disconnected the heater relay for now. Did I fry the glass reed when I soldered the jumper, but that would not seem to matter since I jumpered it. Has anyone else encountered this issue?

The footwell blowers, heaters levers and heater knob worked fine before i did this mod.