So I have a super clean 93 850 93K GLTwith 93K original miles with ECC auto climate control. I'm getting the blinking lights and have retrieved the codes.

Right now the top center vent and passenger vent are blowing ice cold (AC works, just refilled it and you can hear the compressor kick on), the floor is blowing super HOT, none of the temp controls or the middle air mixer control do anything.

I got these codes:
233 Floor Defrost damper position senser open or shorted to 12v
311 Drivers side damper motor shorted to earth
315 Recirc dmaper shorted to 12V
321 Drivers damper motor active too long
325 Recirc Damper motor active too long

Wondering, do I really need to replace all these parts (floor defrost damper, recirc damper, and drivers damper) or is it more likely my ECC unit went crap?

I've been working on cars for some time but am fairly new to volvos. Been researching all day to narrow down this far. Coudl use some advice now. Thanks in advance for any advice.

 

Start by following the diagnostic procedures listed at:

Volvo 850 ECC climate control AC & heater system service manual

Generally when you have codes the best thing to do after noting the codes is to try and clear them to see what returns.

I wouldn't assume the ECC unit is bad if its returning codes so I'd look for something else like a connector, relay, fuse etc first. The ECC set up has like 5 damper motors (ie drivers/passenger, high/low etc. The way the car's heater works is that the coolant always goes through the heater core and the dampers (doors) control the airflow through the core - so if you have full heat, it means the damper is stuck open. Sometimes its the motor, somes it can be the actuator rod. You should be able to access the motors by removing the driver's side panel of the center console.

 

I recently went through some of the same symptoms and i DID NOT have to replace anything, hopefully you are this lucky as well...

Behind the glovebox there are two dampers, REC and FLOOR/DEF. The female motor shaft of the FLOOR/DEF had a corner snapped off. Since it is a square male/female junction, the male end would just spin inside the female. I found the broken piece laying on the bolster. I simply fit it back together and used a small hose clamp to keep it together. It has been holding up well.

I did take apart the damper motor and clean/regrease the gears. Hooked it up to a 9v battery(reverse the polarity as well) and make sure it moved freely. The motor was fine. What you have to be careful of when putting it back together is that the action of the motor is set to one extreme(FLOOR or DEF), I honestly forget which. And then when you insert the damper motor shaft back into the female, it is on the SAME extreme(FLOOR or DEF) by manually adjusting the female end. I will admit it was a little tricky getting it to line up. Also, as soon as you turn the key the motors will go through their positions, so before you put it all back together, test it.

The second issue was my driver's side Vent Damper motor. Somehow the external gears had gotten misaligned. I took it off and repositioned them, this was also a little tricky.

My REC damper motor was fine so I cannot help with that, but maybe a fix mentioned above will work.

I apologize if this is kind of vague since I am working from memory when I fixed it back in January 2015. I do remember setting the three ECC dials to certain positions (as described in the greenbooks) before testing the fixes and resetting the codes.

CHEERS

 

Also, since you're new here, welcome!

this site has helped me out A LOT with all of my Volvos (240/940/850).

800 Series | K-Jet.org

Good luck!

 

Thanks guys for all the info. I will get to it this wek for sure. Such a crazy system they used and obviously ahead of their time, but like all ***** weird techy over done stuff when it breaks, PITA to fix. Its a beautiful 850 GLT with only 92K and mint leather. Definitely want to get this working right. I'll start diggin in soon and update, I'm sure I'll have more questions lol.

 

I also have a vibrating tensioner pulley on the drive belt system. Rattles, and when you turn on the AC it rattles even worse. I have the longer belt wrapped around the alternator so I don't think thats the issue. Maybe just needs a new tensioner. Seperate post material for sure.