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Tech Article: Running Footwell Blowers After Removing Engine Blower

A number of us with 3.2 Carreras have eliminated the engine blower for the heat, but want to keep using the footwell blowers. In stock configuration the footwell blowers need the resistance of the engine blower running to get the blower relay to turn the footwell blowers on. Some individuals have wired a switch in to run the footwell blowers, but I wanted them to operate as they do when the engine blower is in place. It has been suggested that a resistor could take the place of an engine blower. A couple of members of this board tried Radio Shack type resistors, but they burned up almost instantly. Then John Walker and Wavey suggested perhaps using a ceramic ballast resistor such as the type used on some older American cars to reduce voltage to the ignition points. Sounded worth a try so I got the parts and went to work. Went to the auto parts store and told them what I needed and they sold me a ceramic ballast resistor for $8.00. It came with a hole through it that I could use to install the resistor where the engine blower used to fit on the intake manifold. You will also need a 6mm bolt a couple of flat washers and a lock washer. Also a couple of wire connectors. Here is a picture of everything needed:




The small brass screws and nuts came with the resistor. Here is another picture showing the resistor inside the ceramic housing.
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Kurt
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Gone, but not forgotten: '86 Carrera, '72 911E, 2001 Boxster

Last edited by Rot 911; 10-23-2004 at 06:22 PM..
Old 10-23-2004, 05:52 PM
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Ok, now locate the wire and plug that went to the engine blower:


As you can see with the power running it draws around 12 volts"



Now cut off the plug and crimp on a couple of connectors:


now connect the wires using the brass screws and nut. Doesn't matter which wire goes to which side. I figured the resistor would get hot so I made sure the connector did not touch the ceramic housing:
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Kurt
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Gone, but not forgotten: '86 Carrera, '72 911E, 2001 Boxster
Old 10-23-2004, 06:06 PM
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Continued: Thought I would see if it worked before I bolted the resistor down to the manifold. Turned the heater knob all the way on and the blowers fired right up! My suspicions of the resistor getting hot was confirmed. It gets red hot as you can see in this picture. In addition the ceramic housing gets hot enough to burn your fingers! A bit of smoke came of the resistor when it first heated up, but quickly dissipated:



Here is the final installation. I let the footwell blowers run for about 10 minutes without the engine running. I estimate the ceramic housing gets around 200-300 degrees. The aluminum manifold acts as somewhat of a heat sink, but doesn't even get warm. With the engine running the air being drawn into the engine compartment will also help to cool the resistor. As you can see there is nothing close to the resistor that can be damaged by the heat. The wires to the resistor got warm, but not overly hot.
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Gone, but not forgotten: '86 Carrera, '72 911E, 2001 Boxster
Old 10-23-2004, 06:18 PM
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Nice Kurt, but I thought I was the Gruppe B Director of Thermal Testing and Development
Old 10-23-2004, 06:29 PM
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Couple of more pictures showing the final installation:

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Kurt
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Gone, but not forgotten: '86 Carrera, '72 911E, 2001 Boxster
Old 10-23-2004, 06:32 PM
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excellent work Kurt,much appreciated as l`m in the midst of backdating myself.l was planning to use a 3" inline fan to take the place of the engine mounted blower though.Placement of the unit is a work in progress and once l get all my turbo ancilliaries fitted l`ll have a better idea if l can even do it. l really don`t want to lose on HVAC operation and due to my A/C l`ll only be using the driver side air vent from the fan shroud.l think an inline fan should bring operation up to at least as well as stock.l still need the conversion part that goes off the shroud to allow the plumbing to connect to the heat exchangers.l may just give up and buy the factory part from a 930 if l have to..
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Old 10-23-2004, 06:34 PM
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Kurt... did you bail on the thought of getting this working by 're-wiring'? I seem to recall a thread recently where it was explained how to do this...

found it...
Pulled engine heater blower, now footwell blowers won't work!

-bernie

Last edited by einreb; 10-23-2004 at 08:02 PM..
Old 10-23-2004, 07:54 PM
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Nice work Kurt, but one suggestion.

Does not the load of the blower fan simply key the blower relay which in turn supplies power to the footwell blower relay (pin 4?). Why not simply jump that line instead?

Tim
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Old 10-23-2004, 08:18 PM
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Wow, that is great. I am sure glad I did not have to go through any of that when I backdated.

Jeff
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Old 10-23-2004, 08:52 PM
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Will my '77 have the same issue? I'm in the process of getting all the backdate parts for my 3.2. I'm not sure if I even have footwell blowers.
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Old 10-24-2004, 06:47 AM
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Quote:
Originally posted by einreb
Kurt... did you bail on the thought of getting this working by 're-wiring'? I seem to recall a thread recently where it was explained how to do this...
found it...
Pulled engine heater blower, now footwell blowers won't work!
-bernie
I have considered that option, but this took me about 10 minutes to do and I didn't have to mess with the wiring in the auto heat control.
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Old 10-24-2004, 07:05 PM
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Quote:
Originally posted by Tim Polzin
Nice work Kurt, but one suggestion.
Does not the load of the blower fan simply key the blower relay which in turn supplies power to the footwell blower relay (pin 4?). Why not simply jump that line instead?
Tim
Tim I tried that, but all I could ever get to happen is that the footwell blowers continuously ran whenever the ignition was on.
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Old 10-24-2004, 07:07 PM
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Quote:
Originally posted by Silveresrty911S
Will my '77 have the same issue? I'm in the process of getting all the backdate parts for my 3.2. I'm not sure if I even have footwell blowers.
The SC doesn't have footwell blowers.
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Old 10-24-2004, 07:09 PM
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Quote:
Originally posted by Kurt V
I have considered that option, but this took me about 10 minutes to do and I didn't have to mess with the wiring in the auto heat control.
Easy for me to suggest, eh? My car is now functional with "backdated heat"... thanks to a ceramic ballast resistor . I just need to pretty up my fiberglassed backdate part a bit.

Nice write up!

-Bernie
Old 10-24-2004, 07:14 PM
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Wow, thanks Kurt, very nice work! I'll bet you got a lot of gold stars when you were in grade school. I'm inspired to try yet another pair of footwell blowers, or better yet find a more durable replacement, and get that blower out of the engine compartment.
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Old 10-25-2004, 12:40 PM
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Nice project!

Joe
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Old 10-25-2004, 12:50 PM
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Thanks Kurt. Wiring has always been close to alchemy or some sort of black magic to me. Now I can focus on building the block off plate.
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Old 10-25-2004, 01:30 PM
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That really makes the engine compartment look much cleaner.
I am very tempted to follow, and great write-up too.
In terms of heating is it about the same?
Defrosting or defogging concerns?
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Old 10-25-2004, 02:51 PM
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Quote:
Originally posted by goat
That really makes the engine compartment look much cleaner.
I am very tempted to follow, and great write-up too.
In terms of heating is it about the same?
Defrosting or defogging concerns?
I switched to SSI's and have seen no decline in heating and defogging abilities.
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Old 10-26-2004, 06:06 AM
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Thanks Kurt for the confirmation on the blowers, get write up and Pics!
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Old 10-26-2004, 06:44 AM
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