HVAC erratic - Mercedes-Benz Forum
 
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post #1 of 6 (permalink) Old 07-23-2018, 06:30 AM Thread Starter
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HVAC erratic

On my 85 380SE, 139000 miles, bought new, there is intermittently no fan response to the HVAC console pushbuttons. The compressor does appear to engage properly but the fan does not come on regardless of which button is pressed. So far it has always spontaneously recovered and works completely normally including a/c when it does function. The malfunction seems erratic and random. The HVAC control unit is all original to the car. Any thoughts would be appreciated.
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post #2 of 6 (permalink) Old 07-23-2018, 06:31 AM
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Does it work, but just blow through the defroster and footwell?

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post #3 of 6 (permalink) Old 07-23-2018, 07:03 AM
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Check the fuse. It should be in a separate fuse holder. They tend to crack and not work reliably. The crack can be hard to see. If your fuse is still in the fuse box, it isn't up to the task, which could also be the problem. (That's why they've been moved...)

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post #4 of 6 (permalink) Old 07-23-2018, 08:20 AM
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This sounds like the old ignition switch problem.

My fan would randomly cut out. I finally wiggled the key one time when it was happening. Fan started right up. I replaced the ignition switch and no more problems.

Turn the key as far left as you can without turning off the car and also to the right and see if that fixes it.
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post #5 of 6 (permalink) Old 07-31-2018, 08:44 AM Thread Starter
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Thanks for the responses, I will check those things. When the fan does work, the entire system is normal, air vents all put out air when they should. Kent at Mercedessource says the problem is often the fan motor itself, especially the motor brushes which wear down by this age/mileage. Fortunately, the blower assembly is easy to extract above the passenger footwell in a 126, much harder in some other models. I will check that also.
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post #6 of 6 (permalink) Old 07-31-2018, 09:54 AM
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Power wire to the fan was loose on mine, and finally fell off the spade. After i changed the blade fuse, wiggled the ignition I went to the fan motor and found issue. Made the spade clip tighter on the power attachment.


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