rookymatt

iTrader: (15)

Could also be the pressure switch for the a/c, if it doesnt read the pressure right, the electric fan wont come on correctly.

john banks

If the fans are already on full speed with the AC off they cycle on/off.
If the fans are already on full speed and then the AC is turned on they stay on.
If the AC is off the fans don't come on at low speed to cool the engine coolant, they do nothing and then eventually come on at high speed.

This suggests to me that the pressure switch for the AC is not the culprit, and it is more the fans not working, do you agree?

hodgy0_2

the fans on my old golf were two speed fans -- the low speed circuit blew, so i just bypassed it and wired everything to the high speed one

rookymatt

iTrader: (15)

Very much so, sounds as hodgy says also, Fan stage 1 output has failed.

john banks

That works on the Mk4 or earlier, trying to find out about the Mk5, people say it is different (either PWM driven or CAN bus) but I can't find specifics.

rookymatt

iTrader: (15)

Could still be the electric fan john. Why not get a scrappy one and plug it in to see if it starts turning at the lower speed you require. Coming to think of it, just make sure the condenser air flow isn't blocked by dead leaves and debris like crisp packets etc.

john banks

No debris, all works great with the same fans running at high speed.

Problem with a scrappy one is getting the right type, I can't find any info on the connections to the fan.

Hopefully the dealer will be able to help more now I can convince them that other identical cars do have these fans runnning

john banks

This is going from bad to worse. I told the workshop foreman/manager that two other identical cars have their fans on at low speed with AC on and then he tells me they must both be faulty and that the battery would flatten at idle if the fans were on. I suggested that it would be at 14.4V at idle like every other modern car with an alternator but this is apparently different, so I'll have to get the voltmeter out to prove this. I'm taking it in next Wednesday, all I want is someone to fix the fans so I don't overheat my aircon causing more damage and have to drive around with a hot car at low speed on warm days. He simply won't acknowledge that every modern aircon system on a car has a fan running when the aircon is on.

rookymatt

iTrader: (15)

Any mechanic with half a brain will tell you, a quick way to see if the electric fan is running ok is to whack the a/c on and see if it kicks in!

Exactly how much smack does this manager take before he goes to work??

john banks

It is quite frustrating and wasting a lot of time to try to sort out.

I wish I could get more details on where the controller is for the fan speed, PWM, CAN bus, relay etc.

john banks

I hate getting dirty, but in the end I thought it was the only way

Unplugged the fan and there are two pairs of wires, two heavy gauge and two narrow gauge. Both had about 14V across the with the engine running, but the car threw no fault codes with the fans unplugged and the engine running (obviously the fan speed is not monitored and it depends on high coolant te perature to throw a fault). So I plugged them back in and the fans worked as they should. Perhaps putting the multimeter in the connectors had freed them up, but it still works after plugging/unplugging and jiggling it around. Also checked the (unlabelled) relays and made sure they were seated OK.

hodgy0_2

i see sir

you just pulled the plug off, then put it all back together and it works, is that right sir

john banks

Yes sir! And I got dirty doing it

rookymatt

iTrader: (15)

Bit like a pc............"siht, it's frozen"...........remove plug and plug back in.......pc works............"i should get a job in IT!"

Glad it's sorted!

NotoriousREV

Typical modern garage; if it doesn't throw a fault code they've no idea how to trobleshoot. Good old fashioned diagnostics to the rescue, which is what I'd expect from a doctor