924Board.org

[chrisvs]

Gents

I noticed after a ride on Friday that my cooling fan would not come on in my toofah. I am getting only about .1 volts at the fan lead. Has anybody seen the fan relay cause such a result?

After testing and checking voltages at the fuse box, I am thinking it might be a bad wire instead of the relay. I don't think it is the resistor (for the "ignition off side" of the circuit) seeing as I don't have voltage with the car on or off (and the thermo switch jumped, of course).

Any ideas, or is there anything I am missing?
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1978 924 4-spd

[fiat22turbo]

Likely the ground at the forward frame rail, or a ground behind the fuse panel, on the firewall.

Time to get out the sand paper and vaseline to go over your grounds to remove any corrosion and seal them from further corrosion with the vaseline.

Even if that doesn't solve the problem, it will remove a potential issue, allowing you to focus on further potential issues (like a bad relay, bad connections at the socket, etc)
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

[ideola]

I would encourage you to follow the troubleshooting regimen at Clark's Garage. The procedure listed there for the early 944 is accurate for our cars as well.
http://www.clarks-garage.com/shop-manual/cool-01.htm

The one thing that that procedure fails to address, however, is the possibility of a wiring fault. It is possible to have a fault in the wiring on either side of the fan relay. So if you go through the procedure there and it still doesn't solve the problem, you then need to diagnose the entire circuit.

For wiring diagnosis, my advice would be to start with the ground as Stefan pointed out, as well as the connectors at the fans themselves and harness in the engine bay, as these are subject to all kinds of abuse. I recently had an issue on one of my cars that was due to a dodgy repair performed by a previous owner to one of the wiring harness at the fan, so be on the lookout for that kind of stuff.
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erstwhile owner of just about every 924 variant ever made

[chrisvs]

Thanks for the quick feedback!

I did check the grounds, to no avail. They all seem to be in pretty good shape. I pulled them and cleaned them just to be sure.

The next step will be to test the relay. I am definately not getting the 6v through the "igition off" circuit, as I tested did the thermo switch test of shorting the two leads. That is where I measured voltage toggling between 0 and .1 when the leads were jumped.

Now, I also think that my car has the early location for the resistor on the on the upper rad mount. There is is a rectangular resistor there, which I am not sure what is for. I just found that info this morning here on the forum, so I will check that tonight as well. I have not been able to find a picture of anything similar, but I will post a pic tonight for future reference.
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1978 924 4-spd

[fiat22turbo]

Check the connectors on the back of the fuse/relay panel, they like to corrode and overheat and eventually fail if the corrosion is bad enough.

Disconnect the battery and clean the connections on the fuse/relay panel while you're in there.

You could simply have a bad or failing relay, a quick tap on top might jog it loose. If the percussion method of repair works, then replace the relay and verify all works normally, including the temp switch on the radiator.

I believe the resistor allows the radiator fan(s) to run at less than full speed, after the ignition is turned off.
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

[Ozzie]

The relay bypasses the resistor to allow the fan to run at full speed. If the fan doesn't run at slow speed when the thermo switch is bypassed then a power or wiring fault is suspect.
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Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

[ideola]

[jason c]

Check the power wire for continuity and resistance. You can also junp the relay for testing purposes. Where were you placing the ground lead of your tester, the chassis? If so, this would eliminate the factory ground wire as a reason for low voltage.

[ideola]

The fault in every case has been a complete break in the yellow wire. Easy to determine the lack of +12V at the passenger fan connector, not so easy to trace it back to where the fault lies. Fortunately for me, in all three cases, the fault was within 12" of the fan connector, in the section of the harness that contains only the three wires for that connector. If the fault were further up the loom, it would be a real bugger to chase down.
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erstwhile owner of just about every 924 variant ever made

[jason c]