In general, I do not believe these controllers are interchangeable. I would have to defer to an expert parts-guy for a final answer. Here are pictures of the unit I fixed from an '87 W124 300D. Controller part number is 124 830 18 85.
//steve

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And here is a picture of a failed electrolytic cap from the '87 controller. The molded case has failed and leaked....this is what made fault finding by inspection much easier. If you replace these with polarized electrolytics that you find at radio shack, make sure to observe polarity markings on the new part when installing.
//steve

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Thanks Steve. Both of my capacitors look like yours, with degraded top coatings.

I did swap out the control units and currently have the 88 installed and it is seemingly working OK. All fan functions, AC-Heat and vent selection controls work indicating that there is interchangeability between at least some years and versions of the CCU.

From what I can tell, it seems as if in 88, the circuitry technology got better allowing for better space utilization and or size efficiencies allowing all of the components previously housed on the top board to be combined into a single board assembly. Otherwise functions and controls stayed the same. I'll need to see if the 86-87 control unit part number was superseded or not.

Either way I still intend to refurbish my original unit, as it is in far better shape overall than the 88 design.

I went to Radio Shack and boy has their selection of electronic components gone down
I could not find much to choose from. There was a 35VDC 22uF cap and a 35VDC 47uF cap available. From what I understood the original is a 33uF cap. I understand that the regulator needs 22uF minimum, but will a 22uF cap work or is that just too small? Is in that case a 47uF cap too large?

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Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)

I wouldn't recommend the 22uF [nominal] part. With tolerance, temperature variation, etc. you might end up with unstable regulator behavior which you don't want. The 47 uF 35V part will work OK. Remember to figure out polarity on the board wiring and install the capacitor accordingly.

Thanks, will keep the polarity in mind. I believe the board itself is marked + by one side of each capacitor. Is this the correct reference? Or do I need to determine the polarity at the regulator and trace that line out? Sorry, I'm willing to take on the task, but I aint no electrical engineer.

So how much capacitance variance is critical? If the 47uF would work in place of the stock 33uF or does that delta lead to other downstream problems? Just curious for future reference.
TIA

__________________
Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)

Too much capacitance on the input side is no harm. You could put 22 and 47 in parallel if you're in doubt.

__________________
Cheers!
Scott McPhee

1987 300D

A single 47 uF cap will be OK. Regarding polarity, the positive side of the cap must be connected to the trace that leads back to the voltage regulator integrated circuit. [LM2940]

Recently, the ACC in my 87 300TD (124-830-18-85) would not function at all until up to 20-30 minutes into a car ride. I knew the temperature sensors were good, and everything would function properly after it eventually kicked on. After months of freezing temps and no way to warm the cabin up, I finally had the idea to bring the ACC unit inside overnight thinking that maybe it had become sensitive to the cold. Sure enough when I plugged it into the car in the morning it worked fine. The next night I left it out in the cold plugged into the car, but hanging out of the console. In the morning I went out and confirmed that it didn't work. I then used a heat gun to warm the unit up and within 45 seconds the unit kicked on and worked as it should. A quick google search led me here and now with two new capacitors, everything works perfectly. Thanks smorelen!

Also, my brother has the same car and ACC unit with exactly the same symptoms. His capacitors (and mine) looked exactly like the one in your photo.

Hello Steve, I know this is an old post but I would love to see those images if you still have them. I am having the same problem with my car, once it heats up it starts to work fine. Winter is coming so it NEED to get this fixed.

Thanks

Might have to pull the ACC and see how my circuit board is doing as well.
Time to do some research

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1998 Ford Escort ZX2 5 speed - 279,000 miles My Daily

1992 Mercedes 300D 2.5 202,000 - Pure junk
2000 Mercedes E320 Black - 136,000 miles - Needs repair

Don't forget to grease the screw and threads on the spring compressor.