Help! Does anyone understand the footwell blower circuit? - Page 5

Mysterytrain · 01-06-2006, 06:10 PM

nice work gentleman! I looked at the reed switch and wondered why the factory decided to use it in the circuit. If there is a delay from when the rear blower kicks on and then the reed switch closes..it has to be minimal. Its a crude logic circuit at best making the rear blower the master and the footwell blowers the slaves. I can't imagine a safety reason..although if you think about it, if the rear blower fails [and we all know they do] you would never know about it because the footwells would just cranked away on their own. If that was the case then the blower heat sensor would be useless and you would never get the additional cooling feature. So, maybe just maybe..it was the factory's way of making the complete system shut down and forcing the owner to attend to it.

dfink · 06:58 PM

OK took another look at all of the circuit diagrams and think maybe the worst that would happen is that if for some reason the system turned on the footwell blowers without the rear engine blower, power would be fed back through the reed switch (jumper) to terminals 5&6 which supply power to the rear fan. The rear fan would then engage probably pulling to many amps for the footwell circuit blowing the fuse and hopefully no other damage. I also think the diagram on page one by mystrytrain shows the switch on 3 & 4 as normally closed I think this should be normally open as the relay closes the switch and completes the circuit to the front blowers. It also appears that since terminal 3 is a powered terminal that the system sends power to the front blowers rather than provides grounding. That would make sense with the explanation that the rear controller provides power for speeds 0,1,2 and a separate relay provides power for high (3). By the way I am not stating that mystrytrain made any mistake as I doubt he made the circuit drawing and maybe it is showing open but is a poor reproduction and appears closed.
As a side note it was stated somewhere in the earlier sections of the thread that the controller had to be properly bolted to the body to work. This is not the case as the outer cover doesn't touch any of the internals and I have tested on my own car that it work not touching anything. Ground is provided through the wiring I believe terminal 2 which goes to the heater levers. As for the speedometer connection, as others have stated the only reason I can see is that there would be no reason to turn on the rear fan at speed to help cool the engine as the main fan is far superior. So if the car is not moving then the temp sensor would turn on the rear fan to help cool the engine.EDIT: (this would be controlled by the on/off logic of the IC chip which actuallydetermines that the rear fan will run) Because I can only remember the rear fan coming on one time due to heat I will retract my statement about the car being off. As the control circuit appears to be powered by the front fuse assembly the car may have to have the switch on to engage the rear fan. The fact that the rest of the system is not switched may just have been an easy way to power the circuit without running everything through the switch. Damn this is getting long... I am not going to think about this one anymore if anyone wants any further pictures of anything let me know as I still have a dead controller to play with. Jumpers Away.........

Mysterytrain · 01-08-2006, 06:02 AM

Quote:

Originally posted by dfink
OK took another look at all of the circuit diagrams and think maybe the worst that would happen is that if for some reason the system turned on the footwell blowers without the rear engine blower, power would be fed back through the reed switch (jumper) to terminals 5&6 which supply power to the rear fan.

This isn't correct. They are two isolated fused circuits. The switched power that turns on the rear blower is also directed to the reed switch. It sits at the switch waiting for the rear blower to draw enough current to create a magnetic field that is strong enough to close the reed switch. Once the reed switch closes the current then flows thru the relay solenoid [only the solenoid, not the FW blowers] then to ground. Thats it. A very minimal additional current draw. A second 12 volt power feed comes into the controller on pin 3 and waits for the relay contacts to close [Yes, thats a normally open switch] when the contact closes that current flows out of terminal 4 and goes to the footwell blower speed switch. As for the speed switch, Positions 1 and 2 [ sometimes zero] send power to the dropping resistors to vary the blower speeds. Position 3 sends power directly to the solenoid of an AUX relay that then directs 12 volts from a 3rd power source to the footwell blowers for high speed operation. The reason for this is that appling the full 12 volts to the footwell blowers direct from the speed switch will burn up the contacts { yes, just like the headlight dimmer switch} So the relay is added to handle the high current.

I haven't dug into the logic circuit that controls the rear blower operation when the car is stationary. But it appears very likely that the rear blower could come on anytime these two conditions are met:
(1) the temperature sensor gets too hot
(2) the car is stationary.

Actually, I lot of modern cars have this feature.

ianc · 01-08-2006, 09:55 AM

I just did this last night and it works great, so allow me to congratulate you as well Ron!

My FW blowers do not come on with no ignition, or with ignit on and heater levers off. With levers up, they come on very slowly at position 0, the same speed at 1, faster at 2, and faster still at 3.

ianc

Mysterytrain · 01-08-2006, 01:37 PM

great Ianc...I was able to figure it out because of the diagrams you posted. I'm going to rewrite the mod and post it again.

Rot 911 · 01-08-2006, 04:06 PM

Quote:

Originally posted by ianc
I just did this last night and it works great, so allow me to congratulate you as well Ron!
My FW blowers do not come on with no ignition, or with ignit on and heater levers off. With levers up, they come on very slowly at position 0, the same speed at 1, faster at 2, and faster still at 3.
ianc

I have the completely automatic heat, no levers. No blowers with the ignition off. Ignition on, very slow at 0, faster at 7 and 8 and a hurricane at 9. Same whether engine is running or not.

efhughes3 · efhughes3's Garage

I'm auto also, my blowers come on with the key on, no motor, but don't work until you get to the red numbers on the dial-7?

Then, when I go from 9 to defrost, they kick into hyperdrive.

einreb · 01-08-2006, 04:09 PM

Quote:

Originally posted by ianc
I just did this last night and it works great, so allow me to congratulate you as well Ron!

My FW blowers do not come on with no ignition, or with ignit on and heater levers off. With levers up, they come on very slowly at position 0, the same speed at 1, faster at 2, and faster still at 3.

ianc

Mine does exactly this with the 5&6 wires removed and the 4 in the 6 spot.

Again... this is the holy grail of oddball porcha fix it info.

dfink · 01-08-2006, 05:20 PM

Mystrytrain: You are correct I incorrectly traced the circuit. Never try to read diagrams at night...... In any case it appears all is well jumping the reed switch..... If you decide you want to try and tackle the IC let me know and I will post a picture of the small side board so you can try to determine the pin outs to the chip.

aj88cab · aj88cab's Garage

Why is it that Murphy follows me around where ever I go.....

I did the reed switch jumper this weekend and my results were baffling. With the jumper installed the footwell blowers run all the time if the car is on. Heater levers up or heater leavers down the FW blowers run if the car is on. Just to check I disconnected the speedo input and the blower temp switch input and they still run.

I guess with all the electronics in that control unit there is alot more going on that meets the eye. If you look at the PCB there are several devices after the reed switch that trace back to the small logic board. Something is closing the FW blower relay. This doesn't happen with the jumper removed. Very strange.

So I did the only logical thing. I put it all back together, dropped the top, and went for a drive.

Looks like I'l be buying a control unit.

ianc · 01-09-2006, 09:27 AM

Andrew, do you still have the rear blower or not?

ianc

rick-l · 01-09-2006, 09:29 AM

Did anyone try putting a few more turns of wire around the reed switch?

aj88cab · aj88cab's Garage

Quote:

Originally posted by ianc
Andrew, do you still have the rear blower or not?

ianc

Yes, I still have the rear blower.

k9handler · 01-09-2006, 09:46 AM

ok...I need some info from you guys and it must be basic for my simple non-electronic related mind. I just purchased a set of footwell blowers, the wire connections with inline fuse, and the green resistor thing that I have no clue where to install.

My goal is to basically install a toggle switch that will allow me to turn on the footwell blowers when I need them. I have the RS tube in the back...so at the moment my heat is pretty much non existant.

How is the best (or the simple) way for me to hook them up?

ianc · 01-09-2006, 09:56 AM

K9, you've got a bit of work on your hands. I'd start a separate thread asking for advice if I were you. I think people in this thread by definition have Carreras and so probably haven't done this conversion, but others with SC's might have.

On a different note, what has anyone done about the squealing on motor startup? My pass side one squeals for 10 secs or so right after it starts. Anyone know what's causing this and how to stop it? I took the motor out and looked at it; brushes look OK, and I put a little oil in the felt ring at the top. Didn't make the noise after that, so I reinstalled, but I'm hearing it on the cold mornings though...

ianc

k9handler · 01-09-2006, 10:02 AM

ok...thanks

aj88cab · aj88cab's Garage

Quote:

Originally posted by ianc

On a different note, what has anyone done about the squealing on motor startup? My pass side one squeals for 10 secs or so right after it starts. Anyone know what's causing this and how to stop it? I took the motor out and looked at it; brushes look OK, and I put a little oil in the felt ring at the top. Didn't make the noise after that, so I reinstalled, but I'm hearing it on the cold mornings though...

ianc

Ian

Check the clearance between the fan cage and the housing. Mine had actually fused together at one point. There might be some rough edges that need to be cleaned up.

Besides the felt ring try a little oil directly on the shaft and bushing. I also got some electrical cleaner (CRC Lectra-Motive or similar) and sprayed the motor to clean it. If I ever get these things to work, hopefully they will stay quiet.

Andrew

ianc · 01-09-2006, 10:27 AM

Hi Andrew,

Thanks for the tips. It sounds to me more like a brush, or shaft\bearing squeal rather than the cage rubbing on the housing. I'll take the thing out and have another look at it to see if I can recreate the noise a little further.

I don't know why your blowers are working constantly, but it seems like for that to happen with the jumper installed, the main relay powering the rear fan would have to be energized all the time, no? Does the rear fan run all the time? Could something be shorting that pin on the relay?

ianc

aj88cab · aj88cab's Garage

That's what is so perplexing. With or without the jumper the engine blower operates correctly.

One odd thing that I have noticed is that (without the jumper) the FW blowers will come on momentarly when I pull up the heater levers then they go off. Occationlly they will run until I get up to about 15 MPH then quit. Even stranger is I tried another control unit and it did the same thing. Go figure

Mysterytrain · 01-09-2006, 12:56 PM

Sounds like some weird wiring. A few questions.. Do the blowers come on at full speed? Can you change the blower speeds? Remember, the FW blowers get power from the engine compartment controller for positions 1 and 2 [sometimes 0]. In position 3 the switch turns on another relay that sends power to the FW blowers from another circuit. If that aux relay [in the trunk] is bad, ie: the contacts fused together..the blowers will run. If terminal 86 of the solenoid on the aux relay is shorted to ground before it goes thru the switch the blowers will operate without the switch being turned to the number 3 position. From what you are saying I doubt the issue is in the controller. Something is intermittant and the vibration of the car may be effecting it. If the car has had a series of owners the wiring might be modified.