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mrgtturbo · Joined: 06 Jan 2003 Posts: 526 Location: Skowhegan, ME

The outcome of my atempts in trying to figure out a cooling fan problem.

Checked all fuses and they all seem good... (though I could not find a listing of the correct fuse).

With the engine warmed up the fans do not come on.

With the AC on fans do not come on.

When bridging the wire connectors at the thermo-temp switch with a voltometer, with the fans pluged in I got a 12+ volt reading.
Without the fans pluged in I got 0 volts.
At the fan with the wire connectors at the thermo-temp switch bridged I got the 12+volt reading again.

Tested the radiator fans off the battery... they work.

So if they are getting the juice, why are they not working, what may the problem be?

Can't be the temp switch... I don't think... It seems the power reading prove otherwise. I included all the info I could. I so hope one of you guys can help me figure this out.

Thanks.

Aaron

BTW... both fans tested out the same.
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81' 931

Alex Roy · Posted: Sun Apr 13, 2003 4:09 pm Post subject:

When you are jumpering the battery directly to the fans, they are getting full power from the battery, when they are powered by the thermo switch circuit they are getting current-limited power because there is a resistor inline with the normal fan circuit. The problem is that the fan(s) have worn out bearings and the fans don't get enough juice with the inline resistor impeding the current.

The exact same thing happened on both of my 924s. The two solutions are to either bypass the resistor so the fan(s) get full current, or get new fans.

mrgtturbo · Joined: 06 Jan 2003 Posts: 526 Location: Skowhegan, ME

Alex Roy · Posted: Sun Apr 13, 2003 4:48 pm Post subject:

bypass your fan resistor under the dash and find out.

mrgtturbo · Joined: 06 Jan 2003 Posts: 526 Location: Skowhegan, ME

Where exactly is that?
My Haynes manual leaves alot to be desired.
And why would this make a differance when the fan plug is getting power with the thermo switch bypassed, but the fans are not working with it?
If I bypass this resistor what will that cange.

I'm not trying to be a pain in the A** I'm just a little confussed at this point.

Hope you understand.
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81' 931

78porsche924 · Posted: Sun Apr 13, 2003 5:20 pm Post subject:

Ohm's law states that v=ir. vis voltage, i is current and r is resistence. At 12.35 volts, if you have 10ohms of reistence, you will have 1.235 amps. If you have 100 ohms resistence you will have .1235 amps. The more the amps, the more torque the fan motor has. The more the voltage the faster it spins. Take out the resistor and you will have only the fans internal resistence which means it will draw a lot more current allowing it to overcome the friction of the worn bearings. As is it doesn't have enough power to do this.

P.S. I think i just failed the physics test on this crap on friday too.

mrgtturbo · Joined: 06 Jan 2003 Posts: 526 Location: Skowhegan, ME

mrgtturbo · Joined: 06 Jan 2003 Posts: 526 Location: Skowhegan, ME

78porsche924--

One more thing out of curiosity...
Am I getting this correct in an auto terminology, (just for fun)?

Volts= speed (of travel)
Amps= width (amount traveling at the speed of volts)
Ohms= resistance (Down-pressure, friction, ect...)

With volts being a constant, (pretty much in a 12 volt enviorment), the higher the Ohms the more Amps are needed to equal the same power apon the destination? So with worn bearing in a fan it could cause the same effect as say adding 20 feet of wire? The volts would be the same but the umph wouldn't be? I know warn bearing wouldn't change the ohms of the fan or the umph that hits it, but this is the same idea right?
Since the knowledge has been presented I figured I'd try to get a further understanding of it for future refferance. I hope you don't mind.
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81' 931

Smoothie · Posted: Mon Apr 14, 2003 1:02 am Post subject:

On AC equiped cars with 2 fans, both fans come on at full voltage with the ignition on for cooling purposes - switched on by that radiator temp switch. In addition, both fans will come on when the AC is turned on. When the ignition is shut off, just the left-side fan comes on and its' current is routed through the resistor to run at low speed. This resisted running only occurs with the ignition shut off. The two fans are on seperarte fuses. I'll look them up when I get the chance.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Smoothie · Posted: Mon Apr 14, 2003 1:39 am Post subject:

For my car ('82) the left fan and antenna are on the 9-fuse panel, #3 (16A).
The right-side (AC condenser) fan is also on the 9-fuse panel and is #5 (16A).
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

78porsche924 · Posted: Mon Apr 14, 2003 5:22 am Post subject:

Volts are a potential difference. Volts is energy that is used up. Current is not. Think of an exhaust pipe. Volts is the pipe size while current is the flow through it. Don't have my physics book with me, it gave a better description. www.howstuffworks.com is a better source of info. all the stuff u want to know and then some.

your wattage(power)=vi. The higher the resistence(and if your resistor is old it might be too high of a resistence because of oxidation) the less the current you will get at the same voltage. To jumper the resitor, you basically put a wire from before the resitor to after it to bypass it.

Paul · Posted: Mon Apr 14, 2003 5:59 am Post subject:

An interesting fact is that the faster an electric fan runs the more current it draws.

So in the case of a vacuum cleaner, when you stick you hand over the hose and the motor loads up, it actually draws less amps then before you blocked the hose.

78porsche924 · Posted: Mon Apr 14, 2003 11:29 am Post subject:

Think of it like your engine. The higher the rpm the more gas it uses.

924martinirossi · Posted: Tue Apr 15, 2003 11:42 am Post subject:

I have posted fuse and relay assignments in the technical section under electrial, then fuse/relay locations.

The resistor should be mounted up under the dash on the metal part of the firewall above the gas pedal. You really have to look for it up there.

1. For a 1980 924 Turbo measure voltage on both sides of fuse #3 on the additional fuse board.

2. Using a jumper wire with clips on it connect one side of the fuse to the grn/yel wire of the resistor. This wire also runs to pin 87 of the fan relay and to the cooling fan.

3. Jumper across the temperature switch on the upper right side (looking from front) of the radiator.

4. The radiator cooling fan should run at full speed.

You can jumper across the resistor and the fan will run at "fast speed" when the engine is off and the temp is too high.

If the temperature switch is good the fan will run when the temp mark passed the third tick mark on the gauge.

If you jumper across the resistor and the fan runs at "fast speed" your fan relay is bad or the wiring/connectors of the relay. This relay is number 1 top left with 4 pins on it.

Michael

numbbers · Posted: Wed Apr 16, 2003 11:26 am Post subject:

mrgtturbo, the thermo switch in your radiator supplies ground to the fans. So, if you still have 12 volts on the switch when it is jumpered, you must not have a good ground going to the switch. You should have ground going to the side of the switch that is not connected to the fans. Try jumpering ground to the side of the switch that is connected to the fans, and your fans should run regardless of the water temp. If that works, just run a new chassis ground to the ground side of the switch and it should work normally.
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1980 924 Turbo