Heater / ACC / fan regulator question - PeachParts Mercedes-Benz Forum

bhanson · #1 11-01-2005, 05:38 PM

After searching, and posting in the tech help board, I'm back to the diesel discussion with my question. I'm hoping someone has an answer or at least speculation...

Currently, my heat will turn on with the fan on HIGH for any of the selected modes on the horizontal pad, and HIGH on either high or low on the fan speeds, vertical buttons. If I press the automatic fan control button in the center of the vertical controls, or set the temperature control for anything other than high, it will immediately blow the #8 fuse.

Here are the details: I have a 1984 300D. The original ACC burned out a strip of the lower-most circuit board, I think because the aux. water pum shorted it out. I re-soldered the strip and put it in. It behaved exactly as it does now, so I assumed the ACC was just dead. I got a spare from Ebay, which again behaves exactly the same. Now I'm thinking something else shorted too in the great extended fuse-strip fiasco, and something other than my ACC acted as a fuse for the aux water pump.

So, I'm curious, anybody know why it runs fine wide open but won't do anything automatically other than blow fuses? Could it be the blower regulator or another control?

Ben

meltedpanda · #2 11-01-2005, 06:22 PM

is your aux water pump working, if it is siezed that may be your problem. Perhaps it is drawing too many amps. Connect 12v direct to it and see if it whirls freely. If this is ok try disconnecting the temp interlock circuit and see if it makes any difference. Should be a temp sensor somewhere around the thermostat housing.
From there I would suspect fan regulator

bhanson · #3 11-02-2005, 07:26 AM

Thanks. I have already disconnected the aux water pump, after the original acc was cooked. I have a spare now and am going to check it out soon. However the problem remains. The old blower was aftermarket and siezed, and I just got an original from an '85 300D junker in the woods. It definitely needs a brushes replacement, as it has to be Whapped! to get it started. It runs great though. Perhaps I'll have to wait for a final diagnosis until I rebuild the motor. Perhaps that will take care of it. I kind of think not, since it blows the fuse so immediately when I try to put the fan or temperature on auto - but anything's possible.
Ben

meltedpanda · #4 11-02-2005, 09:28 AM

What if you disconnect fan and turn on ACC , do you blow a fuse?
Put a tester on the leads that go into the fan and see if you can get different readings for different fan speeds. The fact that the fan must be whapped may be indicative of it drawing too many amps to get started and then the fuse blows.
I think I have a used temp regulator for your car.
good luck

bhanson · #5 11-02-2005, 04:35 PM

That's a good suggestion, I'll check. I'll get back to you on the regulator too....Ben

bhanson · #6 11-10-2005, 03:32 PM

Well, as a conclusion (hopefully) and follow up, I have ended with the following:

The fan most definitely needed a brush replacement. one was down to the limit, and only the copper was holding it in place any longer. I got the kit from Mercedes Source, and replaced them. Ended up having to solder one side back as the tabs that should be holding it were too mangled. My fault, but found a workaround.

Everything worked -------BRIEFLY.

The #8 fuse on my '84 300D melted. It didn't blow. The copper was fine, but the cheap plastic fuse I bought at the local parts store was made of plastic, and the fuse heats up enough to melt it down to slag.

I cleaned out the fuse box, put a ceramic core fuse in place, and I have good heat. All the auto stuff works.

Still have two very minor problems
1) Defrost vent always on. I remember seeing info about this elsewhere.
2) High speed fan setting makes small vibrating noise. I don't mind. It reminds me that I have heat.

Ben

meltedpanda · #7 11-10-2005, 04:00 PM

Quote:

Originally Posted by bhanson

Still have two very minor problems
1) Defrost vent always on. I remember seeing info about this elsewhere.
2) High speed fan setting makes small vibrating noise. I don't mind. It reminds me that I have heat.

Ben

Glad she is working

I believe the defrost flaps work by an actuator that is behind the glove box, not to hard to access, there are kits for the diaphrams. See if you can see them open and close. there is also one above the radio area it too may be involved but I was able to repair mine without dismanteling the entire dash.
The vibration may be bearings or off balance fan blades. One thing that sometimes happens when you replace brushes is that the very small weights that are placed in the fan cage for balance (much like wheel weights) get disloggged or moved