Mandrake wrote:Hi All,
Success! 8)
I got everything sorted today and thought I'd document it here (including pictures) to help out anyone else that may be contemplating the same job...
As I suspected, the ignition switch WASN'T the reason the blower failed completely, the first thing I did was measure the voltage on both sides of F20 (the 30A blower fuse) while the engine was running, and normal voltage was present - so I knew immediately the ignition switch wasn't the problem.
For those that don't know, the blower is easily accessed in the top left of the passenger footwell, by just removing the upper "carpet" material. There are 3 plugs going into the blower - a large red and large black one which are the main power supply, and a 4 pin plug which also includes a large red and a large black wire, and two smaller wires which are control signals.
See the following:
http://homepages.igrin.co.nz/simon/imag ... lower1.jpg
After simply unplugging and refitting the 3 cables the blower started working again, so I realised I had intermitant connections...so I pulled them all out, cleaned and tensioned them and put them back, and its working fine.
However the original problem of intermitant fan speed control was probably still present, so next I tackled the ignition switch. This is what I found:
http://homepages.igrin.co.nz/simon/imag ... lower2.jpg
Yes, thats right, on a car that was only 8 when I bought it, somebody has ALREADY hotwired the blower power to run off the main ignition contacts but without a relay.
Checking with an ohm meter confirmed my worst fears - the original blower contacts on the switch are totally stuffed - randomly varying from a few ohms to a few thousand ohms every time you turn it on and off, so not even good enough to run a relay coil.
The problem with what they've done is that not only will the blower burn out the new contacts eventually if left there, but when it does it will disable the car as there wouldn't be any ignition power for the engine.
(Not to mention that the fan speed varies with the blinkers and brake lights, and the dash lights all dim with the fan coming on)
I ended up doing the relay mod quite differently to the ways described in the various threads, and I think my way is a lot simpler and easier to implement (no extra fuses or runs of wire back to the battery) and probably more reliable. (Not relying on the faulty switch contacts to power the relay coil)
Final result:
http://homepages.igrin.co.nz/simon/imag ... lower3.jpg
The two wires coming from the brown plug going to the switch are cut, extended, and go to the normally open contacts of the relay. (The two black wires in the picture with the taped joins)
The two cut wires from the switch are not live but I taped them up anyway. They are not used on any other switch contacts.
Pin 1 on the brown plug is the seperate supply run from the battery for the blower, and pin 2 goes across to F20 in the fuse box.
To get power for the relay coil, I tapped into the wire on pin 2 of the grey plug - this is the normal ignition switch output that goes to the engine ECU and is live in ignition on and starter mode, but not accessory.
Earth for the relay coil I took from a large bolt to the right of the fuse box. There is a convienient place to mount the relay on the side of the bonnet pull bracket which has plenty of clearance from other objects.
The consequences for this approach (compared to others) are:
a) The blower runs from the correct 12v feed from the battery - both pin 1 of the brown plug and pin 1 of the black plug go back to the battery unfused, but they are seperate runs of cable, and if you run the blower from the black plug the voltage drop that it causes will affect all other accessories such as dashboard lights, blinkers, power to the engine ECU etc. Also the blinkers, stop lights etc affect the fan speed.
When the blower runs from the brown plug this interaction doesn't happen, because the voltage drop the blower causes only affects the blower, and the voltage drop the lights cause don't affect the blower.
b) Using pin 2 of the grey plug to power the relay coil means you're not relying on dodgy contacts to run the coil - the downside of this is that the relay will also be on in starter mode as well as ignition on mode.
In actual fact this is not a problem because the fan controller will not activate the blower until the engine is started and has been running for a couple of seconds anyway - it never tries to run the fans during starting the engine, so it's a non issue.
c) No seperate fuses required - F20 of the fuse box is still the fuse that runs the blowers, so if the blower fuse blows you're not taking apart the steering column to replace the "extra" fuse fitted there with the other methods...
Hope this is of use to someone. And note that this only applies to Mk1 Xantia's. (Mk2's already have a relay for the blower)
Regards,
Simon