Radiator fan not coming on

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sonne
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Radiator fan not coming on

Post by sonne »

I'm trying to sort the aircon on my polo 9n but i have a problem with my radiator fan as it is not spinning.
It only has the one fan and i found it had a broken wire so i repaired that, tested it and it spun on high or low i'm not sure which one but when i tested the other it just made a clicking sound and nothing happened anyone know what this clicking sound might mean?
Also the compressor spins continuously even when AC is not turned on. There is no air con gas in the system, when i plug on a gauge on the low valve it reads 0 pressure.
I've also tested the fuses and all are fine, i haven't let the engine run idle till 90c yet to see if it spins I will try that tomorrow.
RUM4MO
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Re: Radiator fan not coming on

Post by RUM4MO »

First thing to understand is, the AC compressor on that car is continuously driven, and it has variable displacement, so tends to be operated at roughly 10% capacity when AC is not asked for, ie switched off or not needed to achieve the demanded temperature.

So, that pulley will always be spinning the compressor shaft - unless that compressor has had an internal failure that has stalled the shaft from turning and in that case the rubber coupling between shaft and drive pulley will fail to protect the rest of the auxiliaries being driven by the belt.

Clicking, that will just be the relay for the fast speed, that fan has 2 power feeds, one, the fast speed via a relay feeds 12V directly to the motor, the other, the slow speed via another relay feeds the 12V to the motor via dropper resistors - and it tends to be these resistors that fail open circuit, and so a loss of fast fan speed.

There are a few "hits" available on youtube mostly under the VW Golf heading - all these cars have the same or very similar cooling fan systems.

Edit:- one other thing, or two, if the system is not got enough AC gas, R134a in it, it will not start to run or even switch on the radiator fan fast speed, also, the pressure sensor on the high pressure pipe is known to frequently fail and it can also stop the AC compressor from working, ie producing cooling even if everything else is okay.
sonne
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Re: Radiator fan not coming on

Post by sonne »

Ok thanks for your reply. I'm going to test the fan today with direct power from the battery to test both high/low speeds are working so that will rule the fan motor out. Next step will be filling the aircon with repair recon with a drop of uv liquid to spot for any leaks before i fill it with refrigerant.
sonne
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Re: Radiator fan not coming on

Post by sonne »

Had another look at the car left it running idle for 20 mins it was reading at 95c on an obd reader. It randomly turned the fan on but only for about 5 seconds then it went off again this happened every few minutes.

I ran the engine and bridged the fan sensor again ran on one mode but just clicked on the other.
RUM4MO
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Re: Radiator fan not coming on

Post by RUM4MO »

That behaviour tends to indicate that the fast speed is working and it is the slow speed that has failed, which makes sense as it is the slow speed that uses the inline resistors that fail. What is happening is, the car heats up to the temperature that brings on the slow fan speed(if it worked), because the slow speed does not work, the car then heats up until the temperature rises high enough to bring on the fast speed fan control - but that fan cools the temperature back down quickly so it switches back off, and then on again for another short period of cooling etc etc etc ---.
Johntheo1
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Re: Radiator fan not coming on

Post by Johntheo1 »

Probably no help but our 2005 Polo (no aircon), the thermo switch mounted in the side of the rad switches at the following temperatures.

Fan Speed 1 ON at 91C to 97C. OFF at 91 to 84C.
Fan Speed 2 ON at 99C to 105C. OFF at 98 to 91C.

If the air con pressure switch isn't starting the fan then the fan is only being controlled by the engine coolant radiator temperature(s) so possibly starting on fan speed 1 correctly.
pedroabni
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Re: Radiator fan not coming on

Post by pedroabni »

RUM4MO wrote: Fri Sep 17, 2021 12:03 am That behaviour tends to indicate that the fast speed is working and it is the slow speed that has failed, which makes sense as it is the slow speed that uses the inline resistors that fail. What is happening is, the car heats up to the temperature that brings on the slow fan speed(if it worked), because the slow speed does not work, the car then heats up until the temperature rises high enough to bring on the fast speed fan control - but that fan cools the temperature back down quickly so it switches back off, and then on again for another short period of cooling etc etc etc ---.
hi, that's exactly what's is happening to mine, i've replaced the fan relay, but the same thing keeps happening "/
RUM4MO
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Re: Radiator fan not coming on

Post by RUM4MO »

pedroabni wrote: Mon Sep 20, 2021 7:55 pm hi, that's exactly what's is happening to mine, i've replaced the fan relay, but the same thing keeps happening "/
Yes, but as the in line voltage dropping resistors are built into the fan assembly, ie its cable, then only replacing that or adding in some suitable resistors will ever solve your problem.

The fan relay assembly was probably performing correctly as it is only switching the power supply to either the fast speed wiring or the slow speed wiring.
sonne
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Re: Radiator fan not coming on

Post by sonne »

Managed to repair the fan tested it both fan speeds slow/fast come on when i short the sensor and both speeds come on when i give it direct power. But it does not spin when i hit the AC button is it not suppose to spin? There is zero gas the AC system so my next step is to top it up with recon repair to check for leaks..
RUM4MO
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Re: Radiator fan not coming on

Post by RUM4MO »

sonne wrote: Sat Oct 30, 2021 3:17 am Managed to repair the fan tested it both fan speeds slow/fast come on when i short the sensor and both speeds come on when i give it direct power. But it does not spin when i hit the AC button is it not suppose to spin? There is zero gas the AC system so my next step is to top it up with recon repair to check for leaks..
That sounds to be it operating, or in your case, not operating when it shouldn't, as the AC system will have detected the low gas pressure, it will not be activating the AC chiller and so it will not need to activate the fan, pressing that button that do nothing as the AC present fault will stop the AC system responding to that button press.
sonne
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Re: Radiator fan not coming on

Post by sonne »

Well just filled it up with gas and voila the fan is spinning and cold air is coming out the vents it's not super cold but just glad it's working now. Thanks for the replies RUM4MO.
RUM4MO
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Re: Radiator fan not coming on

Post by RUM4MO »

Good, Good!
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