When my '86 SDL is first started in the morning, there's a loud "pop" that comes from the right side (near the vent) immediately after the engine turns on. Then it won't do it the rest of the day. Any idea what this could be?

Thanks.

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

What vent?

Sixto
87 300D

I have the same issue on my 420SEL.

Start the car and one of the doors in the hvac system bangs hard. Only happens after the car has been sitting more than a few hours. Comes from the pass side, under the dash.

One of those jobs I'll look into someday. Just a minor annoyance.

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Thank You!
Fred
2009 ML350
2004 SL600
2004 SL500
1996 SL600
2002 SLK32
2005 CLK320 cabrio
2003 ML350
1997 C280 Sport

If you don't have a passenger side airbag, remove the glove box liner (remove 2 screws holding the latch, pull up 7 pins, remove 7 anchors, dislodge courtesy light and shove the deal back into the hole, pull out liner), pull down the insulation material and have a look at the two vacuum pods that move the recirc flap. Disconnect the pods from the bell crank and see if it's moving the bell crank that causes the pop or perhaps the pods themselves pop with a sudden burst of vacuum. I know vacuum isn't a commodity but it's easier to talk about it that way

If you have a passenger side airbag, I can't help you get to the pods :/

Sixto
87 300D

I've had that.

I never looked into it, but my theory is that one of the seals somehow got sticky, perhaps the foam wore away to the point where the adheasive is touching or ?? Sounded like the flap was simply sticking and opened more suddenly when the vacuum was "switched on" by the vacuum control solenoid and enough force built to pull it free.

I considered it more of an annoyance than anything detrimental as the force is limited by the vacuum, regardless of flap position, and it can only move so fast into position with its being a fairly light flap with lots of surface area.

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Gone to the dark side

- Jeff

My car does this too, after the thump / pop from the dash the AC would always get colder. Don't know if this happens when the heat is on... I've yet to drive the car in the cold.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

My 300SEL used to do this...sometimes it would get stuck completely and I would have to turn the system on and off a couple times until I heard the BANG. lol

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Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles

The bang is like feedback - hvac working now......

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Thank You!
Fred
2009 ML350
2004 SL600
2004 SL500
1996 SL600
2002 SLK32
2005 CLK320 cabrio
2003 ML350
1997 C280 Sport

Just see if it spins freely by spinning it with your fingers and see if anything catches (nothing should catch). If so, it might need to be replaced or serviced.

Spin what? What are you even talking about?

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Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles

shertex,

I believe the sound you are hearing is coming from the recirculation flap that sits right behind the glove box. My 300SEL does this sometimes and startles the crap out of me occasionally. But then again maybe it's just random gun fire going off while driving around some of the not so great parts of town.

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BENZSTER

W123, '81 240D, Pastel Grey/Blue Tex
W126, '88 300 SEL, Artic White/Grey Leather