No voltage 2nd stage rear window defogger relay.
 

I'm about to wire my rear window defogger, but noticed that the relay is not giving any voltage on the second stage connection (see pin 3 in diagram below). In the electrical diagram one can see that there exists an "solid state" unit.

I think this is the problem, but what is it for? And how can I get it to work? I need this since I'm going to use these connections to turn on two separate functions. (defogger and motor compartment blower (got no heater controller??)).

http://www3.picturepush.com/photo/a/...40/1903506.png

I have been flogging this issue for about a year!

Having bought two replacement relays with the same results
as you are having, I finally contacted the folks @ Hella.

The issue is that relay #2 on the PC board is not being activated
by the solid state circuitry.

My best guess is that relay #2 is on a time delay, or cycle profile
by the circuitry in order to prevent rear window fracture.

As you can see by the attached diagram, all voltages and ground
are present.

Additionally I verified element(s) continuity.

Resistor R1 is most probably a factory adjusted setting for a
time constant circuit.

Email me and I'll go into the details with you.


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Ah, that makes sense. Thanks for your response and offer gerry50, but I think I can work it out from here on.

I was going to tie all defogger elements together, but that doesnt seem to be too sensible with the potential cracking and all. Than I have to find another way to activate the engine compartment blower, since I got no heater controller (relay). Any suggestions?

Oh, im sorry. I meant gerry 40 off course. Yes, I'm wondering if the separate staging is really necessary? Although, I dont want to take the risks in the winter (with normal temperature I think it makes no difference).

I got a 3.2 and looking at my motronic EPROM it should be around 84.

The two stage is indeed necessary as the center element will not adequately defog your rear window especially if you have a Targa, and live in a very cold climate.

The only time we use ours is on winter trips to the mountains.

However, having friends at, and visited the factory on several accassions, I assure you that the "Porsche Coats" are very thorough folks.

They put that two stage in for a reason.

The earlier 911 (2.7's) had a two position switch on the dash board which,
had time out problems.

Lots of fractured rear windows.

Im a believer myself when it comes to true purpose of components in Porsches. I have a two position pull switch too (besides off), but it is not a targa. However, I will wire it in the correct manner in the near future.

I got a workshop manual (84-89). I dont think its a Bentley.

The heater controller relay and its socket is completely absent, at least the 12 pins version. So is the middle/armrest console. I discovered a bundle of wires and a round relay (5 pins) in the engine compartment fuse box. I think it is and older blower system or so:

bundle towards relay:
red / white (one of the pins of relay, always hot 25A fuse 2 ??)
red / black (one of the pins of relay, always hot 16A fuse 1 ??)
yellow or white / green (bundled, but not connected to relay)

bundle from the relay (only 4 wires)
red / white
red / black
yellow / black (to connector of the blower with brown as ground)
yellow

Questions remain:
- which of the wires is the control wire
- to what should this wire be connected (dashboard temperature slider or something ???)

How about the fresh air blower? I took it out to oil it and after installing it again it blows maximum in all positions. The diagram shows some switches to shunt the resistors. What is that all about?

http://www3.picturepush.com/photo/a/...40/1905261.png

Bad transistor, probably. just check all of the components values/integrity,...replace as necc. Looks to be quite the simplest of circuits.......have you checked (measured) them?

Doyle

dshepp806, if you refer to the fresh air blower (luggage compartment) then there are no transistors involved. The dashboard slider got some slide contacts and the blower got some resistors as you can see in diagram above.

However, what are those switches parallel to the resistors. They seem controlled by nothing??? In my case they are all short circuiting the resistors, since all positions of the slider result in maximum blow.

ok, the whole wiring for the engine compartment heater blower works. However, I still havent figure out what will switch it on (yellow wire).

I read something about the mid 'console' heater levers (red) pulling up will connect the blower as well. I have the levers, but does anybody know where the switch is?

Hello,
I am on the same rampage, my engine compartment blower turns on when turn the key on, and will not shut off until I turn the key to the off position. Relay logic? missing switch somewhere?
eric

Eric, does pushing down the heater flap levers turn off the blower? Do you have a 5pins round relay or a 12pins box relay? In the meanwhile you can pull the blower relay just to shut it up.

I had 2 yellow wires connecting each other near the handbrake lever (going into the beam where the shift couple is). Between the connection a switch should be placed, but I got no idea where that switch should be. Unless, one should have a 'climate' control in the mid console.

ClickClickBoom, comes from the Deer Hunter movie, ala russian roulette, put one in the chamber, spin the cylinder, place against head and pull trigger, more than once if you are crazy! But I digress, I will pull my hand brake lever and fish around in there. Going out now, back in a minute or hour.
eric
P.S. 5 pin round

Got a 5pins as well. What I can remember I wired it as follows

bundle from the relay (only 4 wires)
pin 30 - red / white (alway hot fuse 2 25A engine compartment fuse box)
pin 85 - red / black (switched hot, I have search for one in engine compartment and added a fuse)
pin 86 - yellow (if grounded than blower will turn on, still dont know where the switch is)
pin 87 - yellow / black (to connector of the blower with brown as ground)
pin 87a - not connected


http://www4.picturepush.com/photo/a/...40/1908202.png

Hey,
I pulled the parking brake, no heater wires or switch. Went fishing under the dash, on the 3 lever climate control there is a 12V yellow with red stripe that is hot when the switch is on and dead when the red lever is moved to the right side of the car.
FWIW
eric

Sorry,..I think I was following the first post mentioning no output for the center elements......

Doyle

As to the switches, not sure. Formally (schematically), it would appear to be duty cycle-related or time based,..or it's a poor illustration of something thermally controlled (although that's not quite the schematic rep for such a device.

Time to break out those (blower) schematics,...let's see..........

Doyle

ok, sorry for that. Fortunately, the yellow/red is a candidate. I will have a look later for that. If it's the same I have to rewire pin 85 and 86.

In your case, you should remove the relay and see if terminal 85 or 86 is 'connected' by that yellow/red (put e.g. a lamp on). If it does then the complimentary terminal should --I guess-- be permanent ground. If all checks then I guess your relay is stuck (maybe should check that first).

I swapped the horn relay, same-same, blower on all the time.
I am looking at the Porsche "flow diagrams" and looking for the actual switching signal.
later
eric

Ok, Doyle. That makes more sense:). In the meanwhile it gives 12V so I connected center element to 1st stage and upper and lower elements to the 2nd stage. I haven't checked what the exact interval is of the 2nd stage, but it is on right at moment I turn on the 2nd stage. Any idea what the interval is. Is it a matter of seconds or minutes?

Im sorry Eric. I replied but it didnt came through somehow.

What I would do is measure on the actual relay socket and using the relay pin numbering. This is my guess for your situation:

- 85 or 86 : your yellow/red (see if it toggles with e.g. connect a lamp)
- 86 or 85 : permanent ground (given that 12V above is heater on)
- 30 : red/white always on (fuse 2 engine compartment)
- 87 : yellow/black blower
- 87a : not connected

What I think is wrong in your case is the yellow/red wire not reaching your relay. I only have the workshop manual of 84-89, so this 5pin relay nowhere to find. Guess it's a earlier solution.

If all fails, have a look at the shift coupler "compartment" in the beam in front of the back seats. In my case, yellow wires are disappearing there in the harness (they were pulled through one of the holes of the handbrake, hence, I was referring to "near the handbrake" earlier).

Well,
It looks like the heater fan relay gets it's control signal from the power going to the fresh air blower. There is also a signal through the rear window relay, but I will have to figger that out also.
eric The flow diagrams take a little getting used to.

Connected to the fresh air blower? That couldnt be right.

Im not sure what you mean by the rear window relay, but very recently I happen to have installed a rear window wiper (from a 964). If you have removed that then it's perfect to control your engine compartment blower.

Or are you referring to the rear window defogger? I was thinking of that too initially, but figured that it's not practical. Have both defogger and blower on draws quite some current. Having a 2 stage switch opened other configuration, but understanding now that the 2nd stage is on an interval reduce the possibilities a lot. Furthermore, I dont want to risk any cracks in the window during the winter by connecting all elements together.

Or modify the circuitry of the defogger relay so that there is no interval and only use the center defogger element of the rear window.

Either way it not very elegant. And for you the worse case is that you have to draw a line all the way back to the engine compartment and use an extra switch or so.

I know it sounds kinds crazy. I was trying to figger out where the actual "control" signal comes from. It's not intuitive, the circuit for the powering the heater fan is simple, a couple of wires in the rear regulator panel and a relay. My conundrum comes from trying to find the signal that tells the relay to power up the heater fan.The signal wire on the flow diagram comes from the 3 lever switch on the dash, the rear window defroster switch, and believe it or not the seatbelt buzzer relay.
Eric

Here are some of the "Flow Diagrams" from the FSM:





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http://i71.photobucket.com/albums/i1...d/DSCN7949.jpg
Start drinking before you try to cypher the bad boys out!
eric
P.S. 1975 USA CIS 911

Great!

V4 : Heater blower
J14 : THE relay

Blower
Bottom : red - permanent ground (due to side of diodes, odd color choice)
Top : yellow/black - to relay pin87

relay
pin87 : yellow/black - to blower
pin30 : red/white - always hot (due to side of diodes) via fuse S something
pin86 : red/black - switched hot via fuse S something (due to ignition coil N which must be switched hot)
pin85 : yellow - to the control of the starter B

The seat belt warning (SB) relay J34 is also connected to the ignition/starter switch D. I think it's like this:

Ignition key switch will control the seat belt relay in the following way.

1. Turning on ignition ('rest' position before cranking) the yellow out of the SB relay is actually connected to ground. Since the complementary side of the blower relay is connected to switch hot, it will blow.
2. During cranking the yellow out of the SB relay will provide a hot connection for the relay in the starter. Consequently, the blower relay is connected between 2 hot connections and will shut off (no voltage difference).
3. When the engine is running the ignition key will be in the 'rest' position again and the blower will run again.

Hence, the blower is always on except during cranking! Kinda strange and waste of energy. I think I'm going to wire it differently . . .

The SB relay might also switch some other things off when actual cranking is going on. Because there is a hell lot of connection for a simple seat belt warning relay, even if it has an integrated buzzer:)

Last question:
In the diagram connected to the blower relay at switched hot (ignition coil), there is a blue/yellow wire completely at the right. I got that one too. What is it for?

Hello,
I was at Parts Heaven in Hayward today, chatting with the counterman, he said the heater is switched on by the heater levers being raised. I originally thought the switch on the back of the e-brake was for the light, turns out it is for the heater motor. Gonna play about with it tomorrow. Also doing a oil cooler install, adding hard lines flex lines and a cooler, its kinda cool, aftermarket cooler from the 80's. Will post flicks after I get all the parts sorted out and in position.
Hola
eric

The heater levers next to the e-brake, that is what I found logical. What I could remember is that the connector on the e-brake really switches if the it's pulled. Then again, it was a long time ago.

Oil cooler in the front? They are really pricey or is there a cheaper alternative?

Eric. What did you end up doing about wiring the engine compartment blower?