Technical Marea Electrical Problem

[OilBurner]

Two weeks ago I parked my R reg TD100 ELX at a friend's house and left it there while we got a lift to the airport and flew away on holiday. At the time, all was working well. The car has sat unused in the road outside his house since then.

When we returned last night and drove off home it had developed a couple of electrical faults:
1) The heater fan no longer works (and, seemingly, that is no airflow rammed through the unit either, even at motorway speeds); and
2) The button that is supposed to cause the external temperature to temporarily replace the miles on the speedo display no longer has any effect.

However:
3) The cigarette lighter socket still works; and
4) The air conditioning light on the dashboard works correctly (although the air-con itself no longer does due to lack of fan).

If it makes any difference at all:
5) I had parked up and left the sir-con switch in the on position; and
6) I had also left the headlights 'on' (though they turned themselves off and thus saved the battery); and
7) The rear windscreen wiper had expired on the way to the friend's house with mechanical failure (though everything else worked fine).

I have checked all the fuses under the dashboard and nothing has blown, so I am at a bit of a loss. I do know that the rain was very heavy while we were away (my friend's patio flooded for the first time in many years) but teh car should have been OK on a sloping street.

Any ideas?

Andrew

 

[polecat]

Parking up for a week shouldn't cause a problem so it's a bit strange. The air con unit should have a separate 30A fuse.

All I can suggest is check the wiring behind the dash and re-check the fuses. If that fails try to see if the fan or air diverter flaps have seized.

 

[OilBurner]

I have checked and re-checked every fuse in the car, regardless of what Fiat claims its purpose is; not one is blown.

I have been under the bonnet and removed the heater fresh-air intake filter from under the scuttle. This has allowed me to stick my hand inside the blower unit and it spins without problem.

I cannot see any faults with the wiring behind the dash - i.e. nothing looks to have been disturbed - although I am unable to get access to the rear of the switches on e.g the fan controls to trace all the wiring through. If I had a better wiring diagram than the very basic offering in the Porter manual it would probably help too...

 

[OilBurner]

Stuck underneath the blower is a unit with a large heatsink on it. The heatsink itself resides inside the blower next to the fan. On the unit are two thick wires: one black, one grey. Shorting them out causes the fan to work again

Also on the unit are three small control wires: black, red, blue/black. Looking inside it seems as though these three wires operate a couple of transistors which must together switch very rapidly between the two fat wires, presumably at a frequency that depends upon the position of the fan speed control switch (itself a potentiometer, thus offering a variable voltage for the unit to sense).

Tracing the route of the wires between the two components is effectively impossible (and I have removed most of the dashboard in an effort to do so) and I can only assume that the wiring colours change somewhere along the way (the control switch has red, black, green wires).

My suspicion is that the unit with the heatsink inside the blower has failed. It's very easy to replace (3 screws including the cover) and looks as though a previous owner may already have done so at some time.

Is this a known fault? Has anybody encountered this before?

 

[polecat]

It sounds like a speed control unit, never heard about problems with them before but you seem to have the fault pinned down ok.
Good job, good luck with the repair.

 

[johnson550]

Hi is this the sort of diagram youre after

 

[OilBurner]

That's brilliant, exactly what I was after (assuming its the same on a 1910 TD anyway ). Thank you very much.

Andrew

 

[OilBurner]

For anybody who is interested (e.g. has a similar problem in months/years to come) here's the answer. This applies only to cars fitted with air-con...

To obtain the fault code from the system without paying the dealer to read it for you:

1) Switch off the ignition
2) Set heater control switches to HI | 0 | MAX DEF
3) Switch ignition to MAR position
4) Within 10 seconds:
4a) Rotate fan knob to position 1
4b) Rotate fan knob to position 0
4c) Rotate fan knob to position 1
4d) Rotate fan knob to position 0
5) Watch the display on the speedo (where temperature is usually displayed) and after a few seconds you will see the control box cycle through the error codes.

Using the error code you should be able to get your friendly dealer to tell you what is wrong.

If you cannot get any error codes then (assuming that live and earth connections to the sub-harness are in good order) the chances are that the control box has expired. This was the problem in my case. A control box from a breaker cost me £20 plus £5 postage.

To replace the control box you simply need to remove the centre console (the bit with the gear-lever and handbrake in it) to gain access. The box itself is mounted a few inches in front of the gear-lever, clipped up underneath the ash tray. Its about the size of a pack of cigarettes and is released by pressing in on a tag on its right hand side.

I hope that helps somebody. Thaks again to the others on this forum for helping me to get to this conclusion.

Have fun