Hi, I am new to this forum and new to skoda vehicles as well. I recently purchased an Octavia MK1 with 1.6 AEH engine and a busted auto tranny (Catastrophic diff failure!!!).

Upon replacing the tranny and geting it ready for its first test drive since the tranny swap I noticed the fans did not come on when I switched on the AC. I decided to wait until the car was fully warmed up to see if the radiator fan would engage. The temp reached up to 90 degrees but the fan still did not come on. I then decided to perform some troubleshooting.

 

I tested the fans directly with a 12v source and they both worked which ruled out faulty fans.

I swapped the fan control box located under the battery stand with another unit but problem still persists.

I checked the thermostat to see if it was stock closed and sure enough it was, as the radiator was cool as a cucumber while the block was roasting hot. I removed the thermostat completely just for testing. It will be replaced as soon as I get the fans working.

 

After a bit of researching I found out that the fans on this car are engaged by a fan control unit/switch located on the radiator or at least the low speed side is. I then replaced this twice with units taken from a scrapyard Bora and an Octavia MK1 but the fans still do not engage.

I pulled the plug off the unit and short the 12V source (red wire) with the low speed wire (red/white) and both the AC and Rad fans engaged at low speed. This leads me to believe that the fan control units that I tried so far are all faulty. I find it strange that three units can be faulty. So before running out and purchasing a new unit I would like to run it through you guys to see if I am overlooking something.

 

****Also I am currently running just water in the cooling system. Again this is just for testing and will be replaced once the car is fully functional. Would this have any effect on the fan control unit?

Check the fuses on tip of the battery. There are three of them on the 1.8 but I guess they may be the same on the 1.6. The fuses may not actually be burned either, mine was suffering from bad corrosion on the connectors so pull them out and check them all over

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I did a check and the fuses and holder are in good condition. I am getting power on the fan switch plug and I am also able to short the pins on the plug to start the low speed circuit.

 

Do both fans engage when the AC is turned on irregardless of the engine temperature? I am used to this happening on japanese cars so I am not sure how it works on the skoda.

 

Also does anyone have a wiring diagram of the cooling circuit?

On the 1.8T engine both fans do start when the climate control is switched on.

I assume that should happen on the 1.6 as well.... I was thinking that the fan switch would have been the problem but the fact that both fans don't start with the AC on may indicate the fault lies elsewhere. I am hoping it is something simple.

 

Can anyone point me to a cooling fan wiring diagram that I can use to properly troubleshoot, I believe the 1.8 golf should be the same cooling system.

I have replaced fan switch, AC pressure sensor and radiator fan control unit but the fans still do not engage. I have now given up on this and decided to jumper the 12V to the High speed circuit on the radiator fan switch plug. The fans now engage high speed with ignition on. I may purchase a new fan switch to try in the future but at this point I am completely fedup of this car and just want it to work.

So basically your fans are running at high speed all the time? You'll need that sorted it won't do the fans much good. Is the air con cold? And is the compressor working? If you have no gas in the system I'm sure the fans won't work or not until the engine is really hot.

They will be running constant high speed for now.

 

Original Problem: The fans actually do turn on at all. With the ac turned on both fans remain off. Even when the temp goes up to past 90 the fans still do not come on.

 

The AC system is currently empty so I can understand the fans do not switch on with the AC as a result of that, but even with the engine hot to the point of boiling coolant the fans still do not come on.

 

What I can do is Gas the AC system and retry the original setup to check if the fans work then I guess the only other culprit should be the fan switch....this time I will purchase a new one. Until then constant high speed.....

Yeah your right the fans should constantly switch on and off to to keep temp down.

I would replace the top fuse box or at least remove the top green fuses and clean , replace them.

 

My fuses were not blown either

 

I had the same issues that fans would not come on either with aircon or without under hotter temps.

 

I could actually get fans to engage by pressing on the green fuse. So a change of fuses  a clean of connections and all was ok.

 

Also there is a connection plug on the gearbox for alternator and aircon wires that feed to the main part of loom under battery. That connection can also become bad or intermittent.

 

I found that some bodge it guy tried to bypass this main plug and take wire direct from compressor . So i replaced the wiring and routed it back through that plug/connector on gearbox and touch wood not had a issue since.

I have been through the fuse box a couple times, removed the green fuses checking for corosion or any other signs of failure. Will attempt to clean it with some electrical spray this time.

 

I assumed that the fuses were good when I was able to get 12V on the fan switch connector and also jump the pins from there to engage the fans. But the fact is that I don't know which fuses are for what.

 

Will check the connector on top of the transmission as well.

The fuse on mine was fine from the top. But when pulled you could see the legs were oxidised and the receiver was a bit grubby. Cleaned up with wire brush and a needle file and it started working again. Sadly not until after I had actually replaced the fans. Which is a major PITA to do

Cleaned all connections, fuses, plugs etc and then decided to do a continuity test on the rad fan switch. When the car reached 90 degrees I was able to get continuity on the low speed side which ruled out the fan switch as being faulty. Lost at that point but then...

 

I reconnected the fan switch and let the car idle for a while at 90 degrees and the fans came on!!!

 

Since removing the thermostat after the first overheat with the engine I don't think I allowed the car to heat up enough on my attempts afterwards. I realized that when the car reached 90 degrees it still took about 5 minutes or more afterwards to engage the fans. Also the fans engage for a couple seconds then turn of, rinse and repeat. I may have simply missed this or not let the car idle at 90 long enough.....sigh. The fault seems to be my error in troubleshooting. So it seems the only thing at fault was the thermostat and myself :|

 

Either way it works by temperature now. I just need to gas the Ac then test if it comes on together with the AC.

 

I just have one more question as this type of setup is new to me as most of my experience lies with Japanese cars. What's the point/benefit of having a separate fan switch control the fans directly instead of the ECU using temp reading from CLT sensor to engage the fans? To me this seems to be an extra point of failure.

From what I saw so far it allows the low speed side of the circuit to be engaged even after the vehicle is switched off. I am assuming this would be handy after you had overheated and switched off the car????

On 10/06/2014 at 20:46, Liverpool-Lad said:

On the 1.8T engine both fans do start when the climate control is switched on.

Only my smaller one kicks in ?? Do I have a problem ??

3 minutes ago, Okvrsmk1 said:

Only my smaller one kicks in ?? Do I have a problem ??

Low speed resistor has probably burnt out on the main fan.  Test resistance between pins 1 and 2 of the connector on the end of the wires emerging from the fan motor. You should see a small resistance, I suspect you'll see open-circuit.

Repair is possible with a large external power resistor, see here: Mk.4 Golf/Bora radiator fan fix. | Volkswagen Mark IV Forum (uk-mkivs.net) or here 

https://www.briskoda.net/forums/topic/404143-radiator-fan-repair-courtesy-of-vortex-here-and-uk-mkiv-forum/

 

Thanks wino.. il get it checked out