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Question Let me up, I’ve had enough…

…problems with my footwell heater blowers. I’ve reviewed dozens of threads regarding blowers that don’t work, read many related references from these threads, and studied my Bentley wiring diagrams but I can’t get mine to stop running – even with the ignition turned off.

They continue to run despite having:
Removed the fuses (#2 and #8).
Removed the relay in trunk.
Exchanged relays in trunk (cleaned and gently spread posts -- all my relays are red with same part number).

The blower on the motor works properly – only comes on with ignition and red lever(s) lifted. The front blowers remain on and their speed is still controlled by the three-position switch (I don’t have auto temp system) unless I pull their individual fuses (only used in ’88 and ’89 I understand).

So, do I rip apart the three-way switch? Is there a problem somewhere else? Anyone able to explain the problem to an electrically challenged enthusiast?

Thanks in advance.
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Old 02-14-2004, 01:52 PM
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Are the footwell blowers wired as a "permissive" only when the engine mounted blower is running? I think so...but am not sure.

There is also a temp switch in the driver side heat dump valve in the left rear wheel well..might be an influence.

---Wil Ferch
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Old 02-14-2004, 03:42 PM
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Wil:
Yes they are supposed to be permissive -- should operate only when engine blower is running. I'm not familiar with "heat dump valve". Thanks for responding.
Mike Foudy
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Old 02-14-2004, 04:49 PM
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Do you have a test light or multimeter?
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Old 02-14-2004, 05:48 PM
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I've got test light and multimeter. Use them both periodically to find shorts and determine continuity. Not sure how to test for and cut-off power though.
Mike Foudy
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Old 02-14-2004, 06:27 PM
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Just trying to help...many folks that post here don't have or use test equip. Since you didn't mention any measurements...I was not sure. I just need more info to start with. Clearly you should not have power at the fans with the ignition off so you need to back up the circuit to find where it originates...Where I would start is to go to the relay...ignition off..and pull it up far enough in the socket ( but still connected) so you can measure what is on each pin. That should tell you which direction to go to start troubleshooting the problem. Provide me the readings and I may have a suggestion.
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Old 02-14-2004, 06:48 PM
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I don't know doog poop about the new cars...but since the blower still blows, with the ignition switch off? Maybe start there? See what still has juice, and try to figure out why?
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Old 02-14-2004, 07:05 PM
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Flintstone:
I'll take measurements tomorrow and post 'em. thanks.
Mike
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Old 02-14-2004, 07:57 PM
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Flintstone:
Removed relay and tested continuity. Pin 30 is open to 87a, but none of the others. Installed relay as you suggested and pulled just enough to get probes on pins. With ignition off, I got no readings at all. Had my tester set on 15 DCV.

Thought of something else late last night. The footwell blowers previously were connected with the lever(s) switch(es) because they would go on (at low speed) when lever was raised and their speed was increased by three-way switch. Didn’t realize until doing research on threads that they should only go on when the the rotary switch is turned. Does this make the switches between the seats the primary suspects?

Mike Foudy
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Old 02-15-2004, 09:57 AM
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That is odd. If you have measured correctly and have no voltage at pin 87, yet your fans are running...it seems you have a wiring problem and are getting the power from elsewhere. Sounds like that point is disconnected and the blowers have been wired to another (unswitched) source. Is this a new problem? Have you done any recent wiring work? You should have continuity between your fuse on the footwell blower and pin 87 of the relay socket. Remove the relay and check this.
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Old 02-15-2004, 10:22 AM
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I've had the car for just over a year and haven't touched the fan/switch wiring. I had an '84 Carrera for many years and it had the same heating fan system. I do know that the fans on the '89 would go on with the lever switch(es) because they were noisy when I bought the car. I replaced both fans several months ago.

The problem appeared this last week. On Wednesday I noticed a hum after I turned the ignition off and on Friday the battery was dead. Battery trickle charged fine. I wonder if previous owner monkeyed with wiring (car was once registered in Colorado) to improve heat flow. Searching through threads regarding fans staying on -- I think I found two -- the problem was atributed to faulty relays.

I'm certainly not an electrical guy, but I don't trust the three-way switch. Still can't figure out why or how it gets direct current with ignition off. Glad its a three day weekend, its not a life or death deal here, but its annoying.

Mike
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Old 02-15-2004, 11:06 AM
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I'm an elect. engineer with close to 30 yrs experience and I don't know either...so don't feel bad. If you swapped relays and still have the problem..that is not the answer (assuming you switched the right one). Is it possible you are looking at the wrong relay? That is easy to do and would also explain your odd voltage readings, but that would also mean you removed the wrong fuse #2 (25 amp on 3 fuse panel not main one) in mentioned in your first post. Your 12v to run the fans should be from pin 87 of that relay. Even if something is shorted to that line, you should be able to see 12v at pin 87. If there is no voltage there and the fans are running... it seems you have narrowed it down greatly. Measure for an open between the fuse at the blower and pin 87.
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Old 02-15-2004, 11:36 AM
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my fuse box cover has a legend on it so I'm reasonably certain its correct. also when I first heard the hum I couldn't locate it and had just arrived at work, so i removed each fuse, one at a time, thinking i could identify the problem and temporarliy shut it off. the very quiet hum continued through the removal of each fuse (in the trunk). I guess I should be concerned about lack of protection between power source and switches. I going to tackle switches between seats next. thanks for your direction. I'm learning stuff and that's kind of fun.
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Old 02-15-2004, 11:47 AM
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If your previous measurements were correct (fuse #2 on the small, 3-fuse panel in the trunk..not engine compartment) and you are looking at the right relay, it seems unlikely that the switch (between seats) could be the problem as it's purpose is to decrease the voltage that comes in from your relay pin 87 by switching it through different resistors of the voltage divider (the resistor assembly) depending on which switch position you select. In other words, it is a ground input, not a voltage input. The only voltage it sees is from pin 87. Not only that, but you already indicate the the switch works because it controls fan speed....and that is all it does (via the resistor assembly noted above). That means that your voltage must originate between the resistor assembly and pin 87 of the relay. Otherwise the switch would not change speeds properly. If the information you have provided thusfar is correct, I would concentrate on the connection between pin 87 and the connection to the left fan motor. Good luck.
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Old 02-15-2004, 12:59 PM
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Do they operate normally with ignition off...or only hum?
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Old 02-15-2004, 01:01 PM
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They're turning at low speed. Before I took the upholstered panels off, the sound was like a low hum. They will go to high speed with the three-way switch turned -- even with the ignition off.
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Old 02-15-2004, 03:21 PM
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'89cab, i live in Seaside and love to be electrically challenge by those P-cars. Let me look at it along with your wiring diagram if you want.
Truly, Philippe.
Old 02-17-2004, 08:47 PM
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Had exactly the same problem in my 88 - teh PO had just unplugged teh power at each motor. It mysteriosly went away when I had to change my front blower (defrost) motor - still not sure why or if it will come back.

This is an excellent link to explain the many fan motors and how they work http://www.porschenet.com/bruns02.html
Old 02-18-2004, 09:18 AM
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Actually I think they should come on when the red levers are pulled up. There is a switch that is closed when either of the red levers is pulled up, that switch is the "turn the heat on" switch. Then once the lever(s) are pulled up and the switch is closed the rotary switch controls the speed. At least that's how my '88 works.
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Old 02-18-2004, 09:43 AM
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89cab - If you are still having problems, try pulling the engine compartment blower relay if you haven't already. See item #2 on the photo below. You will have to remove the bolt that holds it to the panel then pull it off the connector.

I think the only way you could have low speed operation of the footwell blowers is if power is coming from the speed control resistor and the only place the resistor gets power on cars with the manual speed blower control is thru this engine compartment blower relay (it is called the "blower control unit" on the attached wiring diagram). And the only way your problem can occur (again-I think) is if a relay contact in this relay is not releasing when the levers are pushed down (off). This all assumes that the wiring is all OK and the fault is with a device.

The diagram is for automatic heater controls. I made some notes on the diagram showing what I think is the circuiting in the manual heater control cars. The notes were based on the info in that most excellent article that Libby-O posted a link to (Thank you Libby and the original author).

If pulling the engine compartment blower relay stops the footwell blowers you have a bad relay unit. These units have a control circuit board and a couple of power and control relays inside. I hope I'm wrong because the relay is about $250.

Good luck
Andrew


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Last edited by aj88cab; 02-20-2004 at 03:44 AM..
Old 02-19-2004, 10:09 PM
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