Jump to content

Welcome to RennTech.org Community, Guest

There are many great features available to you once you register at RennTech.org
You are free to view posts here, but you must log in to reply to existing posts, or to start your own new topic. Like most online communities, there are costs involved to maintain a site like this - so we encourage our members to donate. All donations go to the costs operating and maintaining this site. We prefer that guests take part in our community and we offer a lot in return to those willing to join our corner of the Porsche world. This site is 99 percent member supported (less than 1 percent comes from advertising) - so please consider an annual donation to keep this site running.

Here are some of the features available - once you register at RennTech.org

  • View Classified Ads
  • DIY Tutorials
  • Porsche TSB Listings (limited)
  • VIN Decoder
  • Special Offers
  • OBD II P-Codes
  • Paint Codes
  • Registry
  • Videos System
  • View Reviews
  • and get rid of this welcome message

It takes just a few minutes to register, and it's FREE

Contributing Members also get these additional benefits:
(you become a Contributing Member by donating money to the operation of this site)

  • No ads - advertisements are removed
  • Access the Contributors Only Forum
  • Contributing Members Only Downloads
  • Send attachments with PMs
  • All image/file storage limits are substantially increased for all Contributing Members
  • Option Codes Lookup
  • VIN Option Lookups (limited)

Recommended Posts

I'm trying to understand the outputs of the 997.1 cooling fan control unit. I understand that the fans are a continuously variable type and run in proportion to the cooling water temperature.

 

How is the fan speed adjusted? For example, is the voltage adjusted by the control unit? Maybe 0v to get 0 RPM, to 12v to get max RPM. Or, PWM?

 

I'm interested in using this info to add a manual override to be able to run the fan at max speed by a dash switch (but maybe needing some "smarts" if PWM is involved).

 

Share this post


Link to post
Share on other sites
    You can remove these ads by becoming a Contributing Member.

The control of the fans is realized by a PWM signal via the fan control box, however the operation  is more complex, DME 7.8- CAN (high speed and comfort)-GATEWAY-AC-ENGINE/COOLANT/ENGINE ROOM/OUTSIDE temp. sensors and the board network control box are involved.

Share this post


Link to post
Share on other sites

Thanks RFM.

 

Since PWM is meant to (electrically) safely give the device effectively "less" voltage, or more precisely, less "time" at the nominal voltage, to get the fan the run "wide open", one could just supply it with straight/unmodulated nominal voltage - does that seem right?

 

To do this, I could tap into the 12v that's supplying (because it's got the proper current carrying capacity) (in other words, on the input side of the controller) the controller, and add my dash switch in between this tap-in point and the termination at the fan.

 

This effectively gives the fan 12v 100% of the time, whereas the normal circuit gives it 12v between 0% and 100% of the time depending on what the controller is commanding it to do.

 

Share this post


Link to post
Share on other sites

IF this works, I would add a diode in line between your input and the controllers output to stop any back feed of your 12v into the controllers output. This is on the (not necessarily safe) assumption that Porsche do not use this line for data transfer back to the controller.

Share this post


Link to post
Share on other sites

Thanks jl-c. That's a great idea.

 

Here's a different possible approach. How could I fake out the controller to think that the coolant temperature is "too high"? Could I not feed that voltage (or signal? or resistance?) into the controller and then the fans would run on high? Does anyone have some specifics on the voltage and controller terminal for the coolant temp sensor?

 

Share this post


Link to post
Share on other sites
15 hours ago, floatingkiwi said:

I don't think the algorithm uses coolant temp, only engine bay temp possibly in conjunction with speed and outside temp.

Howdy floatingkiwi, is it possible you're mixing up the engine bay purge fan operation with my need for information about the coolant/radiator/evaporator fan control? I'm needing info or a technique to be able to manually turn on the fan with a switch.

Share this post


Link to post
Share on other sites

What I had done is drilling a hole in the right radiator, tapped thread into it and added a Mercedes temperaure sensor (85 C /185 F ) and spliced it into the fan whirring. 

 

All is working as normal except when the coolants get 85 degrees at radiator, => L +R fan full speed. 

IMG_5364.JPG

IMG_5365.JPG

IMG_5368.JPG

Edited by Rob001
pictures

Share this post


Link to post
Share on other sites
8 hours ago, Rob001 said:

What I had done is drilling a hole in the right radiator, tapped thread into it and added a Mercedes temperaure sensor (85 C /185 F ) and spliced it into the fan whirring. 

All is working as normal except when the coolants get 85 degrees at radiator, => L +R fan full speed. 

 

 

Thanks Rob - this sounds like an idea worth pursuing. Can you draw and take a close-up pic of the MB radiator temp switch tie-in to the fan electrical supply line(s)? I want to make sure I cut/tap into the correct lines. Is your car a 997.1? I may just substitute a SPST switch in the cabin (for the MB temp switch). Did you use a diode to keep the current flowing in only one direction?

Share this post


Link to post
Share on other sites

997.1 just tap into the yellow/ blue wire, no diode needed.

When cut, fan goes to full speed both sides so when connected to sensor the "cut" will then at 85 C 

Share this post


Link to post
Share on other sites
On 10/6/2016 at 8:17 AM, Rob001 said:

What I had done is drilling a hole in the right radiator, tapped thread into it and added a Mercedes temperaure sensor (85 C /185 F ) and spliced it into the fan whirring. 

 

All is working as normal except when the coolants get 85 degrees at radiator, => L +R fan full speed. 

IMG_5364.JPG

IMG_5365.JPG

IMG_5368.JPG

 

This exactly what I need. Do have a year and model of the Mercedes that the sensor originally came from? 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Similar Content

    • By clarksongli
      So recently i got the P480 code.  Fan was running non stop on high.  When i turned the car off it kept running on high so i pulled the fuse and went to bed.  In the morning i threw in the fuse and the fan didn't run.....turned the car on (Cold) and after a few seconds went to high again.  Turned off the car and it ran on high for a while then shut off.
       
      So i had to do a bunch of work anyways so i pulled the fan assembly, here are the steps i've done so far:
       
      AC fan works fine, this is only the main fan.
       
      If i power the fan without connecting to the car (the small wires arent receiving signal) the fan stays off (which i think is good).
      If i measure the car harness side, it shows the standard 12v and 0v on the plug.  The signal wires show ~.3V and 12V
       
      My guess was the 12v was the cause of the fan running.
       
      To rule out the temp sensor i unplugged it, but the 12v signal was still there.  plugged the fan in anyways and it was still running.  I did notice when it was unplugged the car only shows as "normal" temp, it didn't peg to the top like i'd think it would.
       
      Finally i found that F10 is the signal (Fan Final Stage)
       
      Anyone have the wiring diagram or know where this 12v is coming from?  I'm 99% positive it does NOT come from the main coolant sensor.  And i'm also 99% my fan is working correctly, but i don't have the "before" voltage check to know for sure.
       
      Any help would be appreciated.
       
      THanks 
    • By sprocket
      Hello Porsche fans,
      I have just purchased my first 928 and she is a beauty. It's only been a few weeks. Now I'm doing what I love the most which is tinker and make it even more perfect. On a recent cruise, I noticed that the engine temp got really hot (after being idle for a minute or two). I was just around the corner so I went home immediately. The red light litt up as I pulled in the garage. I parked it immediately and turn her off. the previous owner mentioned that the fan should run even after you turn the car off and remove the key but no such thing happen. I also notice that coolant started dripping on the floor. I determined that it was just coming from the reservoir from the overheating.
      with that, I was confused because the fan didn't kick in. I took the car out again today and she seems to stay cool when running at speed (35mph or more). but once again would heat up when stopped at lights or driving at slow speeds. I could not hear the fan kick in at all. But I noticed something strange, the fan inside the car cabin would kick in on bust for about 10 secs randomly. At any point it would just blow at top speed even with the control knob turned off! what's up with that?
      this is my first 928 and I'm looking for some direction. I should also mention that the fan was changed to an electric one. Hopefully that doesn't complicate things too much.
      Any help is appreciated.
      Roch.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.