Coolant fan not running

[Redmonds944]

Hi,
When my car used to get to just before the 3rd line on my temperature gauge the fan would kick in. For some reason it doesn’t do that now and goes passed the 3rd line heading for the red.
I’ve put power to the fan and that works fine but which switch triggers the cooling fan and what’s the best way of testing it?

Regards Rob

[944er]

Early cars and late cars are significantly different. What year do you have?

[walfreyydo]

This is probably the best guide on troubleshooting your fans, depending on what year and whether you have AC or not:
https://www.clarks-garage.com/shop-manual/cool-01.htm

Recommend following that and come back if you have any specific questions not covered in the above guide.

[Tom]

This topic is a great candidate for the 944 Handbook if anyone is interested in working on a guide. . If not it is on my list. In the meantime, some helpful threads here:

https://www.carpokes.com/viewtopic.php? ... tch#p47901

https://www.carpokes.com/viewtopic.php?p=52323#p52274

https://www.carpokes.com/viewtopic.php?t=4177#p46925

[Redmonds944]

@944er - sorry for that, I thought I’d put it in there that it is a 1984 lux, no AC.

@walfreyydo - I found that guide after posting the question. I’ve only had time to look at the relay and found that it’s exactly the same as the fuel pump relay on a Skoda Felicia so have swapped them over as I know the Skoda is good.

Regards Rob

[944er]

You have the simplest configuration in your car. Download part 6 from the 1984 schematic here:

https://www.pelicanparts.com/944/electr ... agrams.htm

The cooling fan portion is on the right. It starts by passing through fuse 3 on the extra fuse panel (check this fuse,) then goes to relay number 1 on the relay/fuse panel. This relay is activated when the ignition is on (and not cranking) and bypasses the resistor that causes the fan to run slowly when you park the car hot. I don't suspect the relay as both the relay and the resistor would have to fail for the fan to not run at all. From there, it goes to the positive side of the fan motor. The ground side of the motor goes to the thermostat, which is inconveniently located just below the upper radiator hose. This is the most likely cause of failure, and the only thing that switches the fan on and off. You can test it by shorting the terminals on it together while keeping your hands clear of the fan itself. I've never done this, so I don't know how difficult it is to get to safely. Finally, the other terminal of the thermostat travels to the ground near the left headlight bucket. All wiring and connectors are possible points of failure, you just have to trace it through.

[Redmonds944]

Hi guys and thanks for the support.

I’ve spent nearly 4hrs trying to work this out this afternoon. I couldn’t get to the bottom of it at first as I’d swapped the relay for one I knew was good but I was getting nowhere. Tested the thermo switch and as far as I could see it was working fine. I then put the jumper wire in the thermo switch terminals and got no response with or without the ignition on and I also test for current but still there was nothing.
Finally I looked at the fuse box and the upgraded fusebox fitted and this is where I found my problem. The spade connection on the back of the upgraded fusebox had come away, once connected I had both the slow and fast fan kick in.
The only question I’ve got now is when does the slow speed fan run as I’ve only ever heard the fast speed running?

[944er]

If the radiator temperature is high enough to engage the thermo switch, the slow speed runs when the ignition is off in order to cool down the coolant in the radiator to decrease pressure in the system. Slow speed is used as this provides the cooling needed to achieve this, with less total battery drain.