Well to cut a long story short, the problem was two fold.
Firstly the low-speed fan resistor was open circuit- this became apparent
when I bypassed the relay and tried the fan direct from the battery.
Nothing.
However the ECU was still not switching the low speed side of the relay,
working fan or not, so I thought I had an ECU fault. ATP tested it and
pronounced it fine. Hmmmm I thought..
Anyhow it turns out that the ECU doesnt / can't switch the relay without a
load on the circuit it is switching- somehow the relay feeds a signal back
to the ecu, and with the resistor o/s it wasnt getting this signal...
For anyone with the same problem a 1 ohm 200w resistor is the baby you want
to replace the factory one, which is part and parcel of the fan- Volvo want
to sell you a complete fan and motor and resistor. This gives the fan about
7v and can be zip tied to the fan cowl in place of the broken one.
Tim..
