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  #1  
Old 12-08-2020, 06:38 PM
Grom
 
Join Date: Mar 2020
Location: San Diego, CA
Posts: 243
ACCII Blower Motor Issue

Hi all, I am troubleshooting an issue with my 82' 300D:

Everything works for 5-15 minutes after the car starts, then the blower motor will not run unless the compressor is engaged. Low, high, or auto, motor will not respond.

I've done a lot of research, and looked into the typical suspects:
-Inspected/replaced fuses
-Checked blower motor, looks like it was replaced by PO this year
-Inspected PBU. No solders broken, but reflowed everything anyway
-Swapped out the resistor, temperature regulator, and fan relay box with multiple junkyard spares
-Soldered new capacitors into a temperature regulator

None of the above worked. Weirdly, if I unplug the temperature regulator (silver box) it fixes the problem, but I loose a bunch of functions of course.

Any ideas? Thanks all.

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  #2  
Old 12-08-2020, 09:14 PM
resago2000's Avatar
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try some contact cleaner
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  #3  
Old 12-08-2020, 11:12 PM
Grom
 
Join Date: Mar 2020
Location: San Diego, CA
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Originally Posted by resago2000 View Post
try some contact cleaner
Thanks, I'll try that from the regulator.
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  #4  
Old 12-08-2020, 11:48 PM
rrgrassi's Avatar
mmmmmm Diesel...
 
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Did you check the wiring? Fan should work independently from the compressor, unless someone wired it incorrectly, trying to fix an issue. Also, check grounds.
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  #5  
Old 12-09-2020, 12:22 AM
Grom
 
Join Date: Mar 2020
Location: San Diego, CA
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Quote:
Originally Posted by rrgrassi View Post
Did you check the wiring? Fan should work independently from the compressor, unless someone wired it incorrectly, trying to fix an issue. Also, check grounds.
I've inspected the harness end of the wiring, but not much else.
Yeah, it's weird that it's operation is tied to the compressor. I did clean up a few grounds today.

Coincidentally, I have another 82' 300D that has the exact same issue. Except this car has no A/C and the compressor is disconnected, so it's not a big deal.

What wiring would you recommend I look at?
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  #6  
Old 12-09-2020, 10:25 AM
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Capacitors are only part of the equation on the temperature regulator box. The original capacitors leak and due to how the board is made, the electrolyte flows down the legs and spreads under the conformal coating on the card and corrodes/rots the traces on the circuit board. I've repaired several of these modules and every single one of them had traces that were broken and eaten away from capacitor electrolyte. Some worse than others. Take a close look at yours, if the traces look "dark" in places, they're probably rotten. The most common symptom is Intermittent blower operation, either no blower except for random times, or getting stuck at say only the lowest speed.
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  #7  
Old 12-09-2020, 12:26 PM
Grom
 
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Quote:
Originally Posted by Diseasel300 View Post
Capacitors are only part of the equation on the temperature regulator box. The original capacitors leak and due to how the board is made, the electrolyte flows down the legs and spreads under the conformal coating on the card and corrodes/rots the traces on the circuit board. I've repaired several of these modules and every single one of them had traces that were broken and eaten away from capacitor electrolyte. Some worse than others. Take a close look at yours, if the traces look "dark" in places, they're probably rotten. The most common symptom is Intermittent blower operation, either no blower except for random times, or getting stuck at say only the lowest speed.
Thank you, this is very helpful. Is repairing one of these traces very difficult? I am quite beginner, with a basic soldering iron.
My main symptom is intermittent blower, so you may be right.
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  #8  
Old 12-09-2020, 12:28 PM
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When the traces get eaten up, it's a chemical reaction that turns the copper into a crystalline material and it no longer conducts electricity, or if it does, becomes high resistance. The solution is to follow the traces (or what's left of them) on the board and solder in wire jumpers to fix the bad areas.
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  #9  
Old 12-09-2020, 07:17 PM
Grom
 
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Quote:
Originally Posted by Diseasel300 View Post
When the traces get eaten up, it's a chemical reaction that turns the copper into a crystalline material and it no longer conducts electricity, or if it does, becomes high resistance. The solution is to follow the traces (or what's left of them) on the board and solder in wire jumpers to fix the bad areas.
I see what you mean now. In this image, I circled where the traces appear dark:

https://ibb.co/K7SGrFC

Not coincidentally, they are both exactly where a capacitor is mounted. (Note, some of the burning was from my poor soldering work. I think there was some of that lacquer substance left and it burned)

I am going to jump those traces and see what happens. Thanks Diseasel!
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  #10  
Old 12-13-2020, 08:28 PM
Grom
 
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Location: San Diego, CA
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Hi all, I am reporting back with a fix, in case someone ever has a similar issue.

After getting 1-2 of everything from the junkyard (Blower resistor, black blower box, silver temp regulator box, push button unit) I proceeded to swap components in and out in many different configurations with no luck.

Well, to get to the point, I had to refresh the silver temp regulator box, AND the push button unit:

-On the temp regulator box, I replaced the capacitors as well as jumped some rotten traces on the board (thanks Diseasel)

-On the push button unit, I reflowed the solders that connect the main board to the wing boards, but this was not adequate. I then went back, and carefully reflowed every single solder point I could get to AND cleaned it very very well.

A few things should be noted:
-Both pushbutton units I had looked just fine to the naked eye. No bad traces, no cracked solders, but there was still connectivity issues nonetheless.
-The deep cleaning was essential. After soldering, the connections were restored, but resistance was still high. Cleaning helped that tremendously.

Anyway, hope that helps someone else. A functioning automatic climate control is a beautiful thing.
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  #11  
Old 12-14-2020, 11:48 AM
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Quote:
Originally Posted by Diseasel300 View Post
... The original capacitors leak and due to how the board is made, the electrolyte flows down the legs and spreads under the conformal coating on the card and corrodes/rots the traces on the circuit board. ...
Thanks. Extremely useful. Like most owners, the climate controls in my 1984 & 85 act erratic. I have a bag of spare TempRegular boxes and swapping usually doesn't help, or just changes the problems. I'll open one and try this. I assume one also has to change the leaky capacitors. What is the best way to remove the conformal coating? Any solvent which makes it easy? Heat?
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  #12  
Old 12-14-2020, 11:51 AM
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Acetone and a plastic scrub brush, followed by a denatured alcohol/paint thinner rinse.
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  #13  
Old 12-14-2020, 12:14 PM
Grom
 
Join Date: Mar 2020
Location: San Diego, CA
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Quote:
Originally Posted by BillGrissom View Post
Thanks. Extremely useful. Like most owners, the climate controls in my 1984 & 85 act erratic. I have a bag of spare TempRegular boxes and swapping usually doesn't help, or just changes the problems. I'll open one and try this. I assume one also has to change the leaky capacitors. What is the best way to remove the conformal coating? Any solvent which makes it easy? Heat?
I used Lacquer Thinner and an acid brush, and brushed it on until it stopped flowing green. Worked well.
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  #14  
Old 12-14-2020, 12:54 PM
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Quote:
Originally Posted by BillGrissom View Post
Thanks. Extremely useful. Like most owners, the climate controls in my 1984 & 85 act erratic. I have a bag of spare TempRegular boxes and swapping usually doesn't help, or just changes the problems. I'll open one and try this. I assume one also has to change the leaky capacitors. What is the best way to remove the conformal coating? Any solvent which makes it easy? Heat?
Removing the coating is *NOT* recommended. In some cases, it's all that's holding the card together. Your soldering iron will punch right through it for de-soldering and re-soldering. Clean everything afterwards with denatured alcohol or acetone and an old toothbrush. Just how I do it, I've been rebuilding modules and control boards for this era of Mercedes and BMW for over 20 years. My day job is electronics assembly/testing/repair. I speak from experience to save you time and frustration.
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'91 350SD - "Jest-D" 176K (Sold 12/20/20)
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  #15  
Old 12-14-2020, 04:30 PM
Grom
 
Join Date: Mar 2020
Location: San Diego, CA
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Quote:
Originally Posted by Diseasel300 View Post
Removing the coating is *NOT* recommended. In some cases, it's all that's holding the card together. Your soldering iron will punch right through it for de-soldering and re-soldering. Clean everything afterwards with denatured alcohol or acetone and an old toothbrush. Just how I do it, I've been rebuilding modules and control boards for this era of Mercedes and BMW for over 20 years. My day job is electronics assembly/testing/repair. I speak from experience to save you time and frustration.
I'll be darned. Thanks Diseasel I had no idea.

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