Discovery. 2 td5 2002 GS pre facelift with air con.

The heater blower has stopped working, 13. 5 volts measured at blue connection of wiring loom and heater motor with the engine running, 12 volts with just ignition on yet when the heater blower is connected to a battery it runs.

No faults logged on the atc ecu.
Tried all combinations of settings on atc, lo to high temperature settings, economy, manual and auto settings.
All fuses in passenger fuse box, 7, 20, 31 ok and useable links in engine fuse box ok.
Blower motor relay and power relay can be felt and heard to work.

The only strange thing is that when the air con unit is turned off there is a reading of -1.7 volts at the blue motor connection.

Has anyone any thoughts as to what the problem is.

Many thanks in advance for your thought.

The usual problems with the heater blower, after you've checked all the fuses etc. are the motor itself failing or more likely the speed controller failure.
The motor can be checked fairly easily with a couple of wires from the 12 volts to check that it runs.
The speed controller is a bit less easy to just check, it's electronic. The best thing to do is just to change the controller, or if you're handy with a soldering iron, replace the controller transistor. You can get them for about a fiver on the bay.

http://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2060353.m570.l1313.TR0.TRC0.H0.XMJ11016.TRS0&_nkw=MJ11016&_sacat=0

When that transistor fails the blower still works at full speed cos then the transistor is bypassed, actually i've tried alternatives but the only one which lasts and works 100% well is the TOSHIBA 2SD1460 ... in this particular case it's something else

ROY SIMPSON said:

The heater blower has stopped working, 13. 5 volts measured at blue connection of wiring loom and heater motor with the engine running, 12 volts with just ignition on yet when the heater blower is connected to a battery it runs.

Click to expand...

did you measure that voltage in the blower's plug while it was connected to the blower or unplugged? cos if it was unplugged it's irrelevant as if there's a bad contact along the circuit that voltage can drop to 0 under the blower's load, if it was connected there must be a bad contact on the blower's circuit between that plug and the blower's winding

Found connection co015/co431 attached to heater matrix, this being the connection of the heater wiring loom to the main wiring loom through which the positive and negative feeds pass.
Voltage readings here were 12 volts across the terminals falling to zero volts when the motor was connected.
Next I wired the blower motor directly to connector co015 and then earthed the negative feed without any effect so concluded that the fault was in the positive feed between the fuse box and co015.
I arranged with my garage when having the car serviced to wire in a fused temporary feed which has cured the problem until I have time to investigate the fuse box where I think the problem lies.

Thanks to everybody who contributed to the solution.

Well done... might be only bad contact at the fuses "legs"... remove the fuse and bend it's legs a bit if no joy it can be at the C0584 or in the worst case a wiring issue between C0584-C0431 or even worst within the fusebox... anyway, you are on the right path

Thanks Sierrafery for your pointers to areas for further investigation when I get time to look but service has thrown up some areas for concern namely brake pads are down to 25% and there is some play in the steering ball joints, not excessive but with a trip to Switzerland, France and Italy in the next month about 2500 miles in total need to sort these out first.