(1988 260E)
I know that this noise is related to the climate control but just curious what I might be able to do to get it to stop. It's especially annoying because I'm certain that this is not the way it behaved when the car was new!

It seems that it is somehow tied in with the blower because the speed will change when our clicks. Somebody want to take a stab at helping me understand what's going on hey and what might need to be replaced? TYIA.

Dale

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Dale

If you pop out the glove box liner and reach down along the right corner of the dash, you’ll find the vacuum switchover valve. It’s a complicated little gadget consisting of a gang of electrically controlled vacuum valves. The valves adjust the vacuum level to the various control pods in the heater box. It’s tough to diagnose, and it could be a bad vacuum pod, bad switchover, bad head unit, or a simple vacuum leak. And then someone’s they just get noisy with age. You’ll have to hunt for the HVAC manual for your car for more specifics.

Thanks for your reply, I appreciate it. I will take a look at that and see if I can make any sense of it!

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Dale

I get the same noise on my '88 190E 2.6 for a couple of minutes on cold mornings, but it doesn't seem to affect HVAC operation, so I haven't dug into it.

Also, I hear a whistling noise, again when cold in the morning that I think is an aspiration blower to detect passenger compartment air temperature. Again since HVAC system operation seems normal I haven't dug into that one either.

The Mercs of that vintage are very well engineered and built, but most everything seems overly complicated. Consider the M103 throttle linkage, and I dread the day that the HVAC system needs more than an evacuation and recharge.

Duke