Hi folks been trying to diagnose this issue the past 2-3 weeks and not really getting anywhere with it. Basically if i turn on ignition regardless of the cars temp and if the aircon is on or off the fans will both come on at low speed. The only way to get them to turn off is to pull the green fuse on the left above the battery. What I have tried so far: - Checked both of the fans wiring and verified they work by bridging the 3pin thermo switch plug, both work at low speed and high speed as expected. - Replaced the radiator thermo switch for new unit. - Tried two different Fan control modules, both experience same behaviour - Replaced AC high pressure switch (3-pin duty cycle switch) - this made no difference - replaced green coolant temp sensor for new VW unit - I have inspected all of the fuses relating to AC / fans, ALL fuses above battery are good and have continuity, fuse 16 is good, fuse 5 is good, fuse 25 is good - I have stripped back all the loom that i possible can for the FCM and the fans themselves to try and find a broken wire, but nothing. If i unplug the 14 pin plug to the FCM the fans will stop - I believe the FCM must be getting some kind of signal to say the aircon is running ??? I have read just about every forum thread regarding the fans and the AC and many of them point back to fuse 16 being blown which will cause the fans to run at low speed - My fuse 16 is good , however with ignition on and even with aircon on when i measure Voltage at the fuse's socket there is no power (which suggests to me there is a break somewhere, same behaviour as blown fuse) ??? fuse 16 is for the AC clutch, I have been measuring voltage at AC compressor wiring with ignition on and aircon on (tried both auto mode, and with no mode selected temp at "LO"), i have no power there either. This is where my knowledge lacks as I have never had a car with Aircon so i have little to no idea where to go from here. Another thing worth mentioning is that the temp gauge on my clocks is dead, no signal at all, I am awaiting new clocks to be coded to the car and i think this may be a factor ??? I know the AC and cooling fans are all tied up with the FCM and its just all just getting very confusing for me - i need some advice from an expert on here. Why are the mk4 fans so over-engineered! im used to the mk2 with one fan and one plug either works or it doesn't cheers folks - ANY advice is fully appreciated !!
