* I scanned for any (analog) codes recently in a '90 300CE, 24v. After scanning every system (there were several codes) I ducked inside the car to turn off the ignition.
* The LED in the recirculation switch in the dash was blinking, a constant even blink, without pauses. After I recycled the ignition, without touching the recirc switch (which was in the off position), the blinking stopped. It hasn't come back on. What was that all about?
* The climate control has a pin in the 16-pin data connection, and the scan tool came up with no faults in that system. What does a constant even blink at the switch mean? There's no apparant code since there are no pauses.
* Where on the factory W124 dvd might there be information on the function of the LED in the recirc switch? I thought there might even be something in the owner's manual, but no luck there.

* I did a google search for recirculation switch hoping to find some posts about the ambiguous blinking light.
* According to an old post by JEFFSR in the thread "300E Jealous or AC Problem" the blinking LED in the recirculation switch (and also in the rear window defrost switch) indicates that the "voltage is too low to provide proper function of the system".
* That sounds credible but 2 problems come to mind. Both the ACC and the rear window defrost are off. And if the ignition switch is just cycled without starting the engine (and a charging output) it seems like the light should start blinking again since the voltage source deficiency is still there.
* I'm sure this is all spelled out somewhere in the Mercedes factory literature but I'm sure I won't stumble over it until I have no need for it.

Low voltage condition
Check alt regulator/brush assembly and OVP relay circuits.

* Arthur, thank you for the response. One of the fault codes I got was #8 from the SRS system, pin 6 of the 16-pin data connection. SRS code #8 is "voltage supply, circuit 15R" which seems to tie in with what you say the blinking recirc is saying. I also got SRS code #3, the "driver's air bag", which sounds more like an effect than a cause.
* If the voltage at the battery is ok with the engine running, I guess I'm going to have to check voltage at the 15R connection at the SRS control unit. Do you know of an easier way to check circuit 15R voltage to the SRS control unit (than by getting into the console)?
* In the same way that the CE light relates to an emissions issue, maybe the blinking recirc light relates to SRS issues. So, maybe it's blinking at the threshhold voltage required to operate the SRS? Otherwise, it would blink when there's a charging problem (and it doesn't). Besides, there's already a warning light for that.

Slow charge the battery over-night and try it again in the AM.

That code could also be power interupt, so I would check the fuse for SRS
[ give it a spin in the holder].... and I would also clear that code.

I don't know if my car's got the same problem, but I noticed that my recirc LED switch blinks every time I run the scan test too. It goes out after I turn the ignition off.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

I'm out of my depth with much of what you are discussing here but as far as the low voltage thing goes, my abs light came on one day and the manual says it can come on if the voltage is low. I have a new battery. Well anyway, one day i started the car with the driver's door open and revved the engine up over 2000rpms and suddenly my courtesy light gets a lot brighter - seems like my alternator doesn't kick in until i do that. So that's my everyday starting procedure but I'm sure its a sign that something is on its way out. I hope this helps maybe...

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'87 BMW 325 convertible (162k + miles)
'87 300E, 144k + miles (sold)
'93 Chevy Blazer (full size), 207K + miles
'89 Sea Ray 390EC, 2 x 454's, 1550 hours...
'85 AMF Sunfish

Olde Towne Portsmouth, VA

Your blinking 1HZ led simply means the ACC is in diagnostic mode.

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2012 E350
2006 Callaway SC560

* Brewtoo, what does "diagnostic mode" mean? Can you initiate a blink-code test (of the ACC) from the recirc switch? If you can, how do you do it? And how can I turn it on at will? If it only starts blinking when the scan tool is connected to the data port, what purpose does it serve?
* I should get a single blink followed by a longer pause since the scan tool found no codes in the ACC, tested just moments before the blinking. And the HVAC appears to be working ok.

Diagnostic mode means that you have successfully attached the scan tool and can read codes.

The LED on the recirc switch does not "tell" you anything of diagnostic value. It just starts to blink at 1HZ when you connect the scan tool. It will continue to blink steadily @ 1HZ until you turn off the key, even after you have removed the scan tool.

Perhaps it is confusing since none of the other computers you can scan cause anything to blink except the scan tool.

Just pretend like the recirc LED is not there...when it starts to blink after you connect the scan tool, it is meaningless. Probably would have been better if they had not programmed it to do that.

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2012 E350
2006 Callaway SC560

* Was the blinking recirc switch used throughout the W124 production run, ending in '95? If so, maybe there's a document in WIS that could clear this up. I haven't found any information in the factory 124 dvd and I no longer have a factory 124 chassis manual (which might have something in gp 54 or gp 83). Since the switch was used in other chassis, maybe the information is stored under a different model.
* Having asked around, the answers fall in these catagories: 1.ACC in diagnostic mode, 2. generally in diagnostic mode (system unspecified), 3. power supply to ACC faulty (rear wind switch will blink similarly if pwr to that consumer is faulty), 4. power supply generally low; i.e. charging or battery problem, and 5. the 2-way pressure switch in the refrig circuit is faulty.
* Good thing the damn light doesn't blink all the time!

Like I said, the 1HZ blink that starts when you connect the scan tool simply means the system is in diagnostic mode.

If yours starts blinking after you connect the scan tool, that is all it means.

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2012 E350
2006 Callaway SC560