Hi
I have been reading up previous posts and it sounds like the resistor pack may be the cause of the blower fan not working at all with our 850. It has the ECC system. Is there any way to short/bypass this to see if the resistor pack is the cause? I am getting lots of codes, 325, 411, 414, 418. Other ways to confirm the cause?
Any suggestions would be appreciated

Thanks
Pete

 

From Volvo:
Heater (blower motor) fan speed is variably controlled by ECC output (power) stage in response to signals from ECC control module. The ECC control module digital control signals vary in length according to required fan speed. The ECC output stage has an electronic unit which receives the digital control signals and converts them to voltage. If there is no control signal or the fan is disabled, the ECC output stage sends a diagnostic signal to inform the ECC control module of the fault.

Since the ECC’s ‘power stage’ is a big MOSFET chip, I don't think there's a definitive method for determining if it’s bad unless you’re an EE with a bench full of test equipment or just replacing it with a known good one. You could bypass the power stage by connecting the incoming power directly to the fan, but that would simply tell you if the fan is working or not. The ECC itself may be bad in your case and, again, testing it requires replacing it with a known good one – or a bench full of test equipment.

My power stage was shot but it looked just fine. Bought a new one and everything was OK. It was an expensive way to test it, but everything I read told me it would be bad. I lucked out!