Yet another blower/ECC question

[5806]

First off I need to express my gratitude to this site and you guys that share your Volvo smarts to people like me. I have made countless repairs to my 850 that have kept it running and driven on a daily basis rather than being sent to the scrap yard with the help of this site. That being said, I have one to run past you guys.

I have a 93 850 with ECC. A couple of weeks ago I was running the AC and smoke starts pouring out of the vents and the blower stops. Pulled the ECC out of the dash and sure enough I have the burned up circuit board. I get a replacement ECC from ebay (used of course) and a brand new power stage/resistor. Plug the replacement ECC in and replaced the resistor, turn car on but get nothing. I then turn the head lights on and I get full blast fan regardless of where the fan slider switch was. Since then I have pulled the blower motor and fiddled with it and put it back in. I can now get the blower to work when the head lights are off. The motor goes up and down when I move the slider switch but when I turn the lights on it goes to full blast and stays there. Incidentally I swapped the old resistor back in with the same results.

I did pull the codes. I had about twenty of them which were from the old ECC. Most of them related to ground and short issues which I'm sure were the result of the burn up, but there were a couple that I thought were tell tale: 411 - blower fan drawing excessive current and 419 - faulty diagnostic signal from blower fan power stage. After I cleared the codes and restarted I got three codes: 321, 323 (relates to damper motor so I don't think it is my current problem) and 419 again. I'm not sure what to think of 419 coming back even after I put a new resistor in.

So here is where I am at: What's with code 419, is the resistor even the problem? I'm thinking the blower is the root of the problem and am probably going to replace it, but I don't want to throw good money after bad if the problem is elsewhere. Also, I'm pretty sure the replacement ECC is from a newer model 850. It has the green connectors in the back, my old one has the yellow ones. Could this have anything to do with code 419? What are your thoughts? Thanks!