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  #1  
Old 05-23-2011, 08:46 PM
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ACC amps burning out

I got the ACC in order (I believe) except for the amp. The one that was in the car had a cold joint so I soldered it and it failed I had another amp that also had some cold joints and I repaired it and it failed as well

It looks like the solder is melting and the back of the PC board and it gets so hot it'll burn you. It has taken several hours for each to fail and it's hot all the time the ACC is on. I have no Idea how to begin to troubleshoot this. I figure a circuit must be drawing too much amperage causing the amp to overheat.

From what I understand, the servo can cause failure of the amp if something gets jammed and the servo motor is still trying to run. I'm sure this isn't the case with mine, it parks and sounds smooth and acts like it should when the amp is working.

Maybe the thermister "sniffer"? It doesn't change without input though... When it's just sitting with the AC running and the temp stable the amp just gets REALLY HOT.

Any input on this one?

I'm out of town with no camera or I'd post some pics.

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Old 05-23-2011, 08:53 PM
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could be the aux water pump burning up the amps
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1979 280CE 225,200 miles
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1976 240D 190,000 miles
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Old 05-23-2011, 09:09 PM
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The pump is spinning fine. I even bench tested it and made sure it was working on the car but it doesn't seem like it comes on when it should. Shouldn't it start turning when the heat is set to max? I'm also pretty sure that the amps were hot with the aux pump unplugged but I don't think the amps started failing until I plugged the pump in.

I'll be sure to check it out. Something IS squirrelly about that circuit. Would be nice if that was it!

Thanks for the help!
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Old 05-24-2011, 09:56 AM
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A lot of folks put an inline fuse out at the aux. pump to prevent the pump from causing problems in the circuit.

There are a few threads on here that discuss when the aux. pump should be on and when it shouldn't. I remember talking about it when I had A/C issues a couple years ago. You may find those threads in a search.
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Old 05-24-2011, 10:40 AM
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Is your ACC the same as what's on an 83 300D turbo with a row of push buttons? I took mine apart to have a look and there are no amps inside, just switches, diodes and resistors. The other high current device that the ACC service is the blower. Make sure it and the connectors going to it are ok.
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Old 05-24-2011, 04:01 PM
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Quote:
Originally Posted by funola View Post
Is your ACC the same as what's on an 83 300D turbo with a row of push buttons? I took mine apart to have a look and there are no amps inside, just switches, diodes and resistors. The other high current device that the ACC service is the blower. Make sure it and the connectors going to it are ok.
nope, different buttons
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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg
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Old 05-24-2011, 04:48 PM
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He has ACC II, which has a vertical row of pushbuttons and a servo. It was superseded by ACC III, which has a monovalve and horizontal pushbuttons.
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Old 05-24-2011, 08:40 PM
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I'm on the road now but last night I removed the amp to look for cold solder joints and didn't see anything terrible. This morning I replaced the amp, started the car (With AC off) and turned it to heat. It went from cold (Where it failed at before) to heat and worked pretty well. Trouble was that it wouldn't go back to cool with thumbwheel input. Stuck on heat again...

I pulled the amp out this morning before work because I'm afraid of running down by battery. (Not sure if this would help or not...)

This afternoon I replaced the amp, started the car (I've been turning the AC off before turning the engine off.) turned the AC on and turned the wheel to cold and the AC came on. It worked great for 165 miles.

I turned the AC off and removed the amp again tonight.

I think I may have plugged drains or something because the car was a little "Swampy" at 4 AM when I got in to go to work. No water on the floor or anything

Any ideas? I think I may have some kind of intermittent circuit in my amp or something.

I never did fool with the aux pump though.
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Old 05-25-2011, 01:08 AM
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1980SD,

Does the amp board for your car have several relays on it? The one for the later system does. If so, you might try to correlate the relays with their high amp tasks. It is possible that this will lead you to the item which draws the excessive amps and causes the board to over heat.

I have had a similar problem with the ACC III version, but have not been able to match the relays to their jobs and no one else seems to know any more than I do, even after several postings.

Good luck.
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Old 05-25-2011, 05:58 PM
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^

No relays on the ACC II amp.

I think I found my "swampiness" problem. Water on the floor by the gas pedal...
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Old 05-26-2011, 01:24 PM
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Any updates, 1980SD????
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  #12  
Old 05-26-2011, 05:10 PM
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Not really. Just been busy. Lotta that going on The AC is working fine and I haven't fooled with the thumbwheel any. Just leaving it on 65

I did clean out the evaporator drain lines today and got about a quart of water out While under there I found the driveshaft carrier bearing is toasty... Plus the shifter bushing on the transmission...

I'll probably straighten that out next week.

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