ACC board diagnostics

[Lycoming-8]

Has anyone done any diagnostics and/or repair beyond just the simple re-solder of all connections on their ACC push button main circuit board? Had to replace the original ACC as it was non functional. I sort of knew what to expect, as the cover over the larger board was somewhat melted. On opening it up, I found a badly scorched section with several of the traces melted. After going over the board and the cable pinouts, it appears that the most damaged trace was the one that fed the auxilliary water pump. This was no real surprise, based on previous comments here on the forum.

So after disconnecting the leads to the pump, I quickly stuffed in a different ACC which had no apparent damage and ran the car several miles to check out system function. It seemed to work pretty well on the heat side, which is all I need right now. However, when I returned home and grabbed the unit to start putting it all back together, I burned my fingers on the board just below a couple of the relay coils. Something was really drawing a heck of a lot of amps. So far I haven't traced out just what the four relays on the large board feed, but with the water pump out of the circuit all that seems to be left are the air circulation fan, the A/C compressor, and the mono-valve.

Any one have any insights here? I could sure use some help.

[sixto]

The AC compressor has an outboard relay and the monovalve draws power to close. If you had heat during your trip, that leaves the aspirator motor as the most likely culprit. Can you tell if yours is turning freely, overloaded or plain stuck? Is it possible for bits of the foam tube to get sucked by the aspirator motor as the foam tube disintegrates?

Is it possible that there's a bad actuator solenoid?

Sixto
95 S420
87 300SDL

[Lycoming-8]

Forgot about the aspirator motor, where is it located? I assume somewhere near the main blower motor. Can I tell if the aspirator is turning freely by some manual method? I'm really not wanting to put power to the ACC board again without fixing the basic problem.

By bad actuator solenoid are you referring to the electrical to vacuum devices that are interposed between the ACC board and the vacuum/lever pod operators?

Thanks for your suggestions.

[sixto]

The aspirator motor hangs off the blower motor chamber. I don't know where exactly in a W123.

And yes, I mean what you described. There's a bank of 6 or 7 vacuum switching valves that direct the operation of the register actuators.

Sixto
95 S420
87 300SDL

[pberku]

With the fan motor running, you can get an idea if the aspirator motor is working, or not by placing 1" x 1" Kleenex against the small intake grill next to the rear view mirror. It should stay in place by the draw of air created by the aspirator motor. If it falls off, than either the aspirator motor is not working, or the tube is blocked.

Phil

[mplafleur]

That aspirator motor draws almost no current. I took them out of both my SDs for R&R. On one of them, the commutator fell apart as it was worn through. Then other one is intermittant. I have to stick my finger in it and spin the vane to get it going. My power supply doesn't even register the current draw, while its running or while stuck.