Porsche Enthusiasts Club Forum

Hi all,

I've just had a fault develop - my cooling fans are stuck on when the ignition is on.
I've done my research online and it looks as though problems are in 2 schools - either permanently stuck on even when the ignition is off (which indicates a temp sensor fault) or only one works instead of 2, or not on at all, which is an A/C or relay issue.

As soon as my problem occurred I thought right, that's got to be a relay. I've whipped it out and taken it apart. It could be knackered but I want to test before spending £80 on a second hand part.

I've got a power probe and multimeter. It looks like I need to close the circuit with the probe and check these individual relays which control M1 and M2 and test those resistors.
Any thoughts please how to test / connect up? I don't want to go buy a new one just to test it.

How can I test this chap? Wiring diagram below:
http://www.clarks-garage.com/graphics/cooling_fan_late_1.jpg

with the ignition off and the fans running all the time its the rad switch, had to replace two so far

just unplug the rad switch and the fans stop its definitely the rad switch

do you have a dual fan relay? I have a known working spare

On my N/A 944 when the fan was off with the ignition off it was the relay, unplugging it stopped it. The N/a only runs one fan though.

Unplugging the relay will stop the fans no matter what, which is what I had to do when in France a couple of years ago ... My tuppenceworth is the same as Mr. Way's in that my experience was a failed rad switch. I was lucky with snagging a spare NOS relay (mine has A/C so it's the big and expensive one) for not very much indeed on Eblaggers so it's worth keeping your eyes open...

No, it only runs when the ignition is ON
I need to test the relay first with a probe, I just am not sure how.

Dual fan with A/C by car it a 1987.

give the relay a whack

if the contacts are stuck? a smack might free them off.

depending on where you are you can use my spare to test, and I just checked the relay for twin fans is £185.00

I'm in denham ub9.

First up i'll get my probe out and test the operation of the relays. If they all click, then i'll check the resistors.
Something must be bad in there somewhere.

I have a spare relay in working order if you need one

It's a pretty complex unit with IIRC 4 separate switching relays under the cover. I tried for quite some time with a plastic probe closing the various gates of the relay trying to figure out what might be playing up and which combinations of relay performed what functions - the A/C being the confusing part as it will run at two speeds according to demand and conditions. I gave up in the end and just removed the relay whenever the car was parked up.

As I said the problem ultimately turned out to be the fan switch but it was compounded by an intermittent fault in the relay. I replaced both and kept the relay for spare. Just for a laugh I changed it over a while back and it worked fine... Go figure!