AC Fan Randomly Stops - Question - Mercedes-Benz Forum
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post #1 of 19 (permalink) Old 08-20-2018, 12:45 PM Thread Starter
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AC Fan Randomly Stops - Question

Have a weird thing going on with the AC system in my ’88 560SL. Using the AC system, it works (fan blows and cold air), then just stops. No more air flow, then it will just turn back on and work fine the stop again. This seems to happen randomly. I have the dial set to all the way cold as it's super hot here in Texas Restoration still in work so I haven’t driven the car too much yet but need to address this soon.

Any ideas or pointers?
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post #2 of 19 (permalink) Old 08-21-2018, 01:57 PM
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I would check your blower electrical connections. One may be loose and vibration from the fan could be causing intermittent operation? Could also be loose at the blower switch?
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post #3 of 19 (permalink) Old 08-22-2018, 03:19 AM
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Common thing, happened to me as well. Your solderings in the AC pushbutton are cracking. Same thing happens to the random CC behaviour. Remove the pushbutton units, disassemble all pieces and resolder all solder points.

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post #4 of 19 (permalink) Old 08-22-2018, 05:56 AM Thread Starter
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Thanks for the suggestions - will take a look and let you know....
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post #5 of 19 (permalink) Old 09-02-2018, 07:45 AM Thread Starter
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well, I took the AC controller unit apart as much as I could (being able to see the solder spots). Most of the insides looked really good. Using a magnifying glass, I found several suspect solder cracks and re-soldered those. Put all back together and no change, dang it.

When I turn on the AC, it will work fine for a bit and then the whole system just stops. Blower motor stops, AC clutch disengages. Then system comes back on, runs a bit, then stops.

Not know this system good, do you all think its the HVAC controller which is the issue? I assume it is as if the High Pressure switch was engaging to turn off the compress, that has noting to do with the blower, as it should never turn off until the button is pushed to turn it off, right?

If the consensus is I need a rebuilt controller, any suggestions for a place to purchase one?

thanks
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post #6 of 19 (permalink) Old 09-02-2018, 07:55 AM
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post #7 of 19 (permalink) Old 09-02-2018, 09:40 AM Thread Starter
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Thanks Roncollo. On your #120, I just took out the (N29/1 Electronic Blower Control Unit) and looked it over. The number 6 pin was a little discolored. So I removed the outerbox and re-solder that connection as it was suspect. Put it back in, turned the key on and the blower will run and run, no issue. That pin gets warm but I think its the high fan setting. But as soon as I start the car, I have the same symptom. The AC system/Blower run fine for a bit (30 seconds) and then turns off (clutch and blower) then comes back on.

Now I will mess with the Temperature Regulator (the silver box what you named as the N22/1 Control unit)
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post #8 of 19 (permalink) Old 09-02-2018, 11:29 AM
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Originally Posted by orbit398 View Post
Thanks Roncollo. On your #120, I just took out the (N29/1 Electronic Blower Control Unit) and looked it over. The number 6 pin was a little discolored. So I removed the outerbox and re-solder that connection as it was suspect. Put it back in, turned the key on and the blower will run and run, no issue. That pin gets warm but I think its the high fan setting. But as soon as I start the car, I have the same symptom. The AC system/Blower run fine for a bit (30 seconds) and then turns off (clutch and blower) then comes back on.

Now I will mess with the Temperature Regulator (the silver box what you named as the N22/1 Control unit)
Did you replace the pin. They are near impossible to clean and they are still available from the dealer for under $5.00.
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post #9 of 19 (permalink) Old 09-02-2018, 12:23 PM Thread Starter
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I did not replace the pin. I was just discolored a bit but not bad. I sanded it with 2000 grit just to clean it up. I took the connector apart and inspected all the female side connectors/wiring connection. Nothing corroded. What I re-soldered was in the box itself at the number 6 connection area. Looked a bit suspect so just re-soldered to make sure all was ok


The blower works just fine. Can run for a long long time. It's only when I start the car that there are issues.


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Did you replace the pin. They are near impossible to clean and they are still available from the dealer for under $5.00.
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post #10 of 19 (permalink) Old 09-03-2018, 01:56 PM Thread Starter
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Well, I swapped out the Temperature Regulator from another car and no change. Thinking it must be HVAC controller that has issues.
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