I'm still trying to figure out why the ECC unit is dead. Usually that happens when the two temperature dials no longer work. Have you tried to wire up your own code reader, so you can read the codes?

Quite simple architecture really: 3 lengths of thin, insulated wire, about 18 gauge and a foot long. 3 large paper clips. and a small light bulb, preferably an LED, but I used a 12V tester lamp (used to test current on 12V systems.
Attach the light to the end of two of the wires. Straighten out the paper clips and attach to the ends of each wire (to make a good probe).
Insert the 2 probes that have the light bulb in to socket #16 (12V) and socket #6 (ECC). Insert the third wire into socket #5 (ground).
Turn the key to position II, tap the ground wire to the top of the other wires. The light will shine brightly, but only do it for less than 1 second. Wait for the answer: 3 numbers will flash, blink the light. With a pencil, write down the 3 numbers. Tap the ground wire again to get the next series of numbers, and continue until the first number flashes again. Turn the key off and remove the probes.
Now, look up the error codes.

The vent damper motors never fail, but they do go out of position when a vent breaks. And that is what causes the errors.