1997 850R ECC climate control not working

[brendonrobar]

I am working on a 1997 Volvo 850R and the automatic climate control is not working. I replaced the blower motor because of an overheated wire that melted it's sheathing. Still nothing worked. I then swapped out the main ecc module (the box with the climate control knobs) and still nothing works. There were blinking ac and recirc lights but now that I've swapped the ecc there are no lights. It's as if there is not even power to the ecc. I checked fuses and they are ok. Does anyone have suggestions? Thanks!

[combatkarl]

Hi and welcome. ECC issues appear to be common and I'm still trying to figure out mine.

If the replacement ECC that has no blinking lights does not power the fan or allow you to change where the air comes out of the vents/defrost/feet vents etc, I'd probably go back to the old ECC that had the blinking lights.

The blinking lights indicate fault codes that can "diagnosed" using a home-made code reader. See post by jreed https://www.matthewsvolvosite.com/forums ... 3&start=14 and Ben850 --> https://www.matthewsvolvosite.com/forums ... 37&t=60660

You may need to open up the dampener motors and clean as mentioned in a response in jreed's post above and also look for a split shaft that the dampener motor turns -- which is covered here --> https://www.matthewsvolvosite.com/forums ... =1&t=54750 and --> https://www.matthewsvolvosite.com/forums ... =1&t=60251

Good luck.

[brendonrobar]

I did put the original ecc module back in the car and now the vent position selector and the ac switch work! The blower fan speed slider causes the "ac power module" which is like the resistor to make clicks as if it's trying to turn on... I'm wondering of that ac power module is the problem. It's the black box with metal fins which stick into the vent to the left of the blower fan. I have not been able to find a used ac power module to test it yet... they cost over $100 new... what are your thoughts?

[jreed]

It could be a bad MOSFET in the power stage that controls the blower fan. If you can get the codes from the ECC unit, they may help identify the problem -- this might be easier than trying to swap parts to see if you can fix the problem without diagnosing the cause.
There was also a good write up by Ozark Lee showing how to test for a failed power stage by grounding a wire to see if the blower runs:
https://www.matthewsvolvosite.com/forums ... =1&t=40168

A few months ago at the junkyard I pulled a power stage from a wrecked car, just in case I might need it later. It was not expensive (~$10) but I haven't tested it yet. You might try a junkyard or ebay for a used unit.

[brendonrobar]

Thanks for the help! The problem was the power stage. I replaced it with a used unit and now the system works!