dlucas

As per earlier posts re heaters I got resistor unit changed on mine now all works fine. See older posts some time ago for for more tips and discussions on this.

But:

Haynes wiring diagram basically shows that heater control switch switches current through a series of resistors (in a resistor pack) to control the speed of your heater fan, on setting 3 a relay kicks in to bypass all the resistors (this is the 'click' you hear when switching from 2 up to 3 - if you keep hearing the click your relay is OK I would think) resulting in max fan speed, on setting two there is more resistance, on setting 1 yet more etc to slow down fan.

The most likely thing (and it is quite common apparently) is for the resistor pack to give up the ghost, this is probably what is causing your problem. A new resistor pack is quite expensive from Volvo (20 quid + I think, try ringing them - I think it is a Volvo only part unfortunatly but I would be pleased to stand corrected - other suggestions welcome!), my freindly independant volvo mechanic fitted a new one for me for 5 quid labour and as I was busy that week and as the fititng was so small compared to part cost I did not DIY it.

Essentially the resistor pack is somewhere in the black plastic heater unit box on the bulkhead, access by unclipping the clips that hold the two halves of this box together. Mechanic I use said you can rewire it to bypass the resistors then you can get fan on speed '3' and '0' at least (which may be cheaper if you have a soldering iron and don't mind reduced fan speed choice!), or you could try a resistor unit from a scrap yard. I took the view that I wanted it working on all speed and a scrap one might just pack up again soon.

If this is not causing your problem, or if you have already changed this, the other thing could be the fan motor has packed up (more unlikely to be honest). Fan motor is attached to said black box in obvious position, you could perhaps test this by disconnecting the wires and using a meter, if you have one, or by disconnecting the wires, putting a 12 volt supply across it and seeing if it works or not (hence bypassing all switiches, relays and resistor packs) to see if this is where your fault lies. I think there are other contribs on here about cleaning fan motor brushes etc to improve faulty motors.

Re your point about it kicking in from time to time, mine failed occasionally about 12 months before it finally went and I (wrongly) put this down to faulty dash switch, since it worked fine for the last 12 months prior to finally packing in I did nothing about it at the time!

I can send you Haynes pages if you give me an address but I don't think it says much more then I have put here, apart from a bit more detail about taking your under bonnet heater box off completley, which I don't think you have to do to change the reistor unit but others may confirm.

You will be pleased when it works again in this weather! Good luck
Dan