I've read many posts on here and other forums about this issue but still haven't managed to resolve it. I picked up a replacement resistor from the scrap yard but that hasn't fixed the issue. It could be that the replacement resistor I got from the scrap yard is also defective but before buying a new one (they are expensive) I'd like to troubleshoot to see if the issue is coming from elsewhere. Here are some of the symptoms and fixes I have tried so far.

1) A/C and Recirculate LEDs do not flash or come on at all.
2) Blower motor on high once key is turned in ignition

Fixes tried:

1) I have tried to switch the J relays around
2) replaced resistor with one from scrap yard

Once thing I have noticed is that the actual ECC unit is defective since none of the lights on A/C and recirculate come on?

 

The resistor is used to control the lower fan speeds and is bypassed when the fan is on full. Have you tested the relay, checked all fuses? Did you test the replacment and old ballast resistor to make sure both are in working order? Its possible the ECC unit has failed so if you have access to a used module from the yard or ebay, that may be the next step.

You may find some diagnostic tests at Volvotips.com (online shop manuals for the 850s and others).

 

I just received a brand new resistor and problem persists so it doesn't come from there. Fuses are good too. Which relay are we talking about? The J relays or the relay that it to the left of the blow motor? Any other ideas before I go to by a ECC unit?