Cooling fan always on full......and aircon leak detection...

nod

Member
hi folks, my project car has been back on the road for about 6 months now and all that time the cooling fan has been on high whenever i drive it. so far with all the lockdown stuff we've just been local in it, but soon its off on a long trip so i want to sort it. I will do a scan, but just wondering if anyone knows the cause. I'm guessing temperature sensor issue ? the car never gets up to temp unsurprisingly. Also, the aircon doesn't work as it has a leak in the system somewhere, thats my other question, finding that leak, any good diy tips? cheers nod.
 
Air con, take it to a specialist who will diagnose the leaks hopefully free under there checks before regassing. Make sure you check what costs are involved if they can not regass the car.
Not a FSI expert but to me that does sound like the temperature sensor has failed requesting the fan on all the time. Perhaps if you remove the wiring plug from the sensor the fan will stop, equally the sensor open circuit may switch on the fan so removing the wiring plug may have no effect. Best to get an FSI guru to answer that fully for you..
 
Isn't no6 in this diagram the sensor that controls the fan?

thanks for the diagrams, the sensor in the bottom hose is where I was thinking of starting my search, so I'll give it a go at the weekend and feedback the results.
the aircon, I took it to my local ats for a regas and they could do it, as they found the leak, couldn't diagnose. I'll see what happens with a local specialist cheers.
 
Another possibility is failure of the fan controller. A VCDS scan would confirm. The most likely culprit for a refrigerant leak is the condenser. If any component in the A/C is changed, also change the dryer.

RAB
 
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thanks for the diagrams, the sensor in the bottom hose is where I was thinking of starting my search, so I'll give it a go at the weekend and feedback the results.
the aircon, I took it to my local ats for a regas and they could do it, as they found the leak, couldn't diagnose. I'll see what happens with a local specialist cheers.

This is a good shout.

When I first bought the car I identified that the thermostat and sensor needed changing and passed this onto what must have been the worst garage in the world.

They had put the green sensor into the blue sensor position - at the bottom of the radiator - and thats the one that controls the fan.

Result was the fan was on ALL the time and I didn't even realise they had been that incompetent but the "mechanics" lack of ability had no bounds.

When changed the fan went into normal operation. Given the price and ease to change its worth a punt - you will though need to have some g12 or 13 on tap.
 
And if you do find the wrong sensor has been fitted double check the pins in the wiring plug are not damaged.
 
Another possibility is failure of the fan controller. A VCDS scan would confirm. The most likely culprit for a refrigerant leak is the condenser. If any component in the A/C is changed, also change the dryer.

RAB
Thanks Rab, do you have a part number for the dryer please?
 
This is a good shout.

When I first bought the car I identified that the thermostat and sensor needed changing and passed this onto what must have been the worst garage in the world.

They had put the green sensor into the blue sensor position - at the bottom of the radiator - and thats the one that controls the fan.

Result was the fan was on ALL the time and I didn't even realise they had been that incompetent but the "mechanics" lack of ability had no bounds.

When changed the fan went into normal operation. Given the price and ease to change its worth a punt - you will though need to have some g12 or 13 on tap.
That's really helpful, thanks. I wouldn't put it past me to do the same! I'll check. antifreeze ready, cheers
 
So I didn't get the sensor s mixed up, but I did get water into the connectors during the project...
IMAG1462_1.jpg

When I unplugged the bottom sensor the fan stopped, I'm expecting this corrosion to be the issue. Cheers
 
Very much does look like it. Chance if you use contact cleaner you may be able to remove at least some of the corrosion. Although you may be better off just replacing the plug.
A thorough clean would require the plug to be disassembled. Special tools are required to release the pins from the plug to do it properly, but am sure someone in the past has carefully inserted something like a sharpened paper clip and released the pins after removing the retaining plate.
 
Just to feedback on this one. I used a pins extraction tool to get two of the 4 pins out of the connector block and they were OK inside. Reassembled and reconnect ed and still the same, fan on high all the time. Unplugged fan off. So next I took out the sensor, temporarily replaced with a same size spare sensor that goes higher up in the block The green type just to prevent too much coolant loss. Looked at the pins of the blue 4 pin sensor and they were heavily corroded , cleaned up with contact cleaner and a small screwdriver to scrape with. Removed green sensor, struggled to reinstall blue sensor ( had 2 orings stuck in the bottom pipe...), got it in , plugged in and sorted. Fan now works as it should. Hope that helps someone. Cheers
 
Another update. After a day, the fault returned. Swapped out for a new sensor and sorted again fan works normally.

The air-con needed a new condenser and new o rings to fix the leak.
Cheers
 
Certainly now worth having a scan and clear old codes. Run and rescan.

And replace the dryer for the climate at the same time.
 
I did have a new dryer ready to install but couldn't shift the nut due to the access, so had to leave the old one in place...
 
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