ECC Defrost Non-Op

mendelsa · Post by **mendelsa** » 02 Sep 2021, 23:01

Hi all,

I've been fighting with the ECC in my '93 850 for quite a while now, and finally have to resort to asking for help

I'm getting codes 2-3-1 and 2-3-3 which are "Ventilation damper motor position sensor circuit open or shorted to power" and the same for the Floor/Defrost damper motor respectively.

After following through the repair manual's procedure for the given codes without success, I opened up the motors per this guide viewtopic.php?f=1&t=27239 finding that both motors work just fine on the bench (powered with 12V, resistances are within spec).
I also replaced the head unit due to a bone-head move that resulted in magic smoke being released.

The behaviour I am seeing is this:
When the ignition is turned on the rec and ac lights flash, and the ventilation damper starts rotating until the damper is in the defrost position (whether it can or not!).

None of the motors seem to move when the central control is rotated, and the vent damper seems to only move when the key is first turned on.

Has anyone dealt with something like this before? I'm very confused since theoretically the motors and the head unit should both be good.

Any ideas or insights are appreciated. Let me know if I can add more detail.

Post by **jreed** » 04 Sep 2021, 06:02

I haven't experienced the exact same problem you're describing, but I have had a few different problems with ECC damper motors and especially the rheometer-type position sensors that are connected to them.
You mentioned that you are seeing the REC and AC lights flash... that's a sign that the ECC unit has recognized one or more faults in the system. Have you tried to read out the error codes stored inside the ECC unit? If not, it's worth doing this to help focus the hunt for the root cause(s) of the problem(s).

Post by **Chuck W** » 04 Sep 2021, 06:52

Have you performed the damper motor recalibration procedure?

mendelsa · Post by **mendelsa** » 06 Sep 2021, 19:04

Yeah, I did pull the codes. Like I say I was getting 2-3-1 and 2-3-3 which correspond to the vent and the defrost damper motors' positions sensors either being shorted to ground or power. But I tested for shorts (per the manual) and didn't find anything.

I did attempt the 9-9-9 damper motor position reset without success. I am definitely thinking that I should try it again but that will have to wait until I have four tires on rims, since the reset requires driving the car faster than 30kph or something for ~15 mins.

Thanks for the comments guys! I'll try the reset again when I can, and post an update.

Post by **scot850** » 06 Sep 2021, 19:29

When you have the motors connected to the car, leave them out of the casing and see if they move ok when you change the position of the air direction on the ECC. Do each one in turn. Some are a devil to get to as you are working blind, in particular on the RHS rear motor.

I had a problem with our 93 man years ago where the main flap stuck in the closed position. It has a foam around the door flap and it had melted over the years making it tacky like glue. The parts are long time NLA. I had to pull the dash and heater unit to open it up, clean the surfaces and fit a thin sticky back foam seal in place of the original.

Also check the drive is not broken on the front motor on the RHS. It can shear off. The black or white plastic end of the shaft has a square hole in it for the end of the servo motor. Due to the issue above and age it breaks off. Sometimes it can be held in place with a zip-tie. That part is replaceable without removing the dash.

Finally, on an 850, take time to remove and clean the 2 cabin temp sensors as a maintenance. There should be one on either side under the roof grab handle above the front doors. You have to prise off the top plastic door trim and then remove the grab handle. The motor can the be removed and cleaned with cotton buds and some IPA (not the bear type!).

Neil.

Post by **scot850** » 06 Sep 2021, 19:33

Should also add, the main cold air intake flap behind the glove box has a plastic arm on it that breaks. Fairly easy to replace but make sure the motor is in the correct position before fitting the arm. You have to remove a T20? screw from the motor and it should slide forward and out. I think the part is the same as the later V/S70's if I recall. It was available still a couple of years ago. Otherwise junkyard.

If you are really stuck and the little cold air damper flap arm is not available PM me. I may have a spare but following house move I am still trying to find stuff!

Neil.