Greetings all,

 

Newbie here with a first post.

The heater & a/c fan in our 1.6TDI greenline (62 plate) has stopped working. The car has dual zone Climatronic ventilation.

All the lights on the control unit come on as usual and you can set the fan speed but there's no blow!

I removed the blower motor without too much trouble. This one doesn't have the (apparently) troublesome resistor pack for the speed control.

Instead it's got a module (p/n VW AG 3C0 907 521F) which contains a bunch of electronics. This module is mounted on the fan housing.

I've disconnected the module from the motor and tested the motor using a bench power supply. It runs fine.

So I guess my problem is either that module is faulty or that the control unit isn't sending the right things to it.

The module has a 5 pin connector, but there are only 4 connecting wires in the cars loom...two fat wires (earth and 14V with the engine running) and two thin wires which I assume are the controls.

 

Does anyone know what signals the 2 control wires carry?

Is this CANbus??

Any ideas on how to test the module?

 

Thanks,

Martin.

Yes it is canbus.

Canbus. OK thanks Graham.

 

Here's today's update.

I put a spot of oil on the motor bearing. Whilst it ran on the bench supply it was stiffer than I would have expected.

Then I opened up the module to see if anything was obviously wrong. (electronics is my background BTW)

There was nothing burnt out, no dry joints or "stressed" components as far as I could see.

I don't have any test gear that 'speaks' Canbus so I could not do any further bench tests so I re-assembled it and put it back in the car.

Low and behold it's now working. Even when I waggle the wires and connector.

Whether that will be the end of the story remains to be seen!

 

For anyone else that's having similar issues I've attached some pictures. The module is available as a spare for £30-40.

Oh, and if like me you didn't know where the fan is ... its above the passengers legs behind a thin sheet of grey foam.

The pollen filter is down there too (this is for RH Drive cars).

 

Will post again if the problem returns!

 

Regards to all,

Martin.

 

 

 

 

 

Presuming that the copper coloured coil is a heat sink, there must be some resistors in there somwhere.

No, it's an inductor. The variable DC voltage to the fan motor is achieved by switching on/off repeatedly at high speed.

Power transistors (N-Channel MOSFETs in this case) do the actual switching.

By changing the ratio of on to off times the effective DC output voltage can be adjusted - that in turn changes the fan speed.

I didn't attempt to work out the circuit, but it's probably a form of "buck converter" (see wikipedia for details).

This method is much more efficient than the series resistors used in the old fan speed controls. ie energy is not wasted in very hot resistors.

 

Yes, there is still some heat generated - those pink plastic sheets in the photos are actually thermal coupling between the PCB and the alloy base-plate.

HTH.

 

Martin.

 

 

I noticed on the second photo from the bottom there appears to be some staining/corrosion to the bottom left corner. But I didn't see anything on any of the other photos to show what that was touching. I'm assuming therefore it was the other side of the heatsink with the pink sheets stuck to it, and it is also the shiny alloy item seen between the motor and the control unit in the second photo from the top.

I'd guess it didn't get manufactured with that staining, which suggests that at some point some fluid had dripped onto that area. From looking at the photos I think it is the end of the module where the red and wires for the motor power plug in. Did you notice any moisture on the fan housing in that area?