850 Automatic Climate Control Failure

[joer]

that is incredible my a/c stopped working and the seal in the ecc was broken and this let the smoke escape,so when i pulled it apart the same zener had pulled out of the board and the same caps were damaged,identical to the pics posted,unbelievable, tell me its not a common fault,the big question is was a repair attempted and did it last

[scot850]

Got to love PnP. I have 2 spare ECC units (for P80 V70's) as I got them on a 50% off sale for $15 each. Both have good bulbs and easy to swap out and test. I only have 2 as I thought one was bad, but found out it was the cabin temp sensor in the dash that was bad.

Based on the age of the units for the older 850's the new components are worth considering if you are handy with a soldering iron.

Neil.

[atucker1]

Very interesting. Thanks for info. I had no fan and flashing lights on ac and recirc, now absolutely nothing and a steady light on OBD 1 port B1. Time to take a look at the control panel.

[jkalmar]

I have the same issue with burn marks in the same location...93 Volvo 850GLT.

To me it looks like the capacitors are installed correctly (polarity-wise), both in your photo's and on my circuit board. What I think may be wrong is that this part of the circuit was under-designed. The copper trace that is burned beside the capacitors was a ground line. My suspicion is that the current got too high on one of the motor controller chips and burned up the copper trace. That left the other chips improperly grounded, with the result that destructive current burned up the rest of the trace.

The capacitors do not show up as short-circuited on my unit and behave properly using a simple analog ohm-meter test...a momentary low resistance measures and then decays to a higher resistance, indicating capacitor charging.

The 5 Toshiba TA8050P motor controller chips are meant to be just about bullet-proof, with thermal protection, over-voltage protection, and short-circuit protection. Likewise, the 78005 (a 5 volt voltage regulator) is protected against short-circuits too.

I'm going to attempt a repair of my ECC computer by restoring proper ground where the burned up trace once ran, both on the front and back side of the board.

On the surface, it appears to me that ALPS or their circuit board maker did screw up, but not by putting the capacitors in backwards. To me, it looks like insufficient consideration given to thermal overload. Then again, the circuit board implementation may have not been up to spec. in that the copper traces may be too thin to support the level of current expected. Either way, it's looking like a thermal issue caused by too much current on the copper trace to me...not a reversed capacitor problem (which I have seen before in other equipment).

My plan now is to restore that grounding trace on the board. Then before I install the ECC computer, I'll cut the wires to the 5 motors/servos/etc. in the wiring harness. I'll then install connectors on each cut wire so I can reconnect each wire.

The idea behind cutting these wires and installing connectors is to be able to install a 12V lamp temporarily in series with the motor. If a motor is short-circuited to ground, in theory, this should cause the light bulb to glow brightly when the computer fires up that motor. [If the motor/servo/etc. is working properly some motor or flap sound should be heard and the bulb should glow less brightly. [I will probably measure the resistance to ground before the light bulb test, to see if anything close to a short-circuit appears.]

I'll let you know what I discover.