Whistling HVAC System? - PeachParts Mercedes-Benz Forum

timreid · #1 05-15-2003, 02:38 PM

My wife told me she has got a couple of whistles the other day, I laugh, sorry I did, then she continued. The whistling noise was when she was driving the 400E, and came from inside the cabin. Yesterday when we were driving I heard the whistle noise (about 1 to 2 seconds) and I believe its coming from the HVAC system. When the noise occurred, I thought it happened when the air distribution was changing in the center vents. A vacuum leak?
Thanks, enjoy your drive, timreid

gmercoleza · #2 10-20-2005, 01:43 PM

Did you ever find the source of the whistle? I am going to look at a co-worker's 97 E320 in a couple weeks. It suffers from something similar, and I believe it is coming from the HVAC unit itself, which I know is big $$$$. I plan on poking around with a MityVac. Any suggestions for where to look? It's definitely manifold vacuum related because it cycles on/off when throttle is applied at varying rates while driving the car.

I know this is one of those things that could take 20 minutes or 20 hours to find...

3star · #3 10-20-2005, 03:53 PM

I'm having the same issue with my W210. A very soft whistling or squeaking noise coming from the climate control vents. Only occurs with the A/C on. Doesn't happen in EC mode. Noise is very intermittant. Usually lasts 3 to 4 seconds at a time. I've had it to the dealer but they could'nt replicate the noise while it was there. Doesn't appear to be a squeaking blower motor.

Larry Delor · #4 10-20-2005, 05:52 PM

I have had this whistle for about a month now. I thought at first it was because of a leaky vacuum hose in the trunk, however that is fixed now, and it still squeals/squeaks continuously. I do believe mine also stops when the controls are turned to Off.
I'm curious as to what this might turn out to be!

manny · #5 10-20-2005, 05:55 PM

Are your dashvents COMPLETELY open ?

skiier3_9 · #6 10-21-2005, 01:25 AM

I had a similar problem in my e320 BUT it would only happen when one or two of the dash vents were partially or fully closed. Check your vents, make sure they're open (at least to test the whistle).

jcyuhn · #7 10-21-2005, 09:43 AM

You can make a 210 whistle by closing the right or left side dash vents. But that's a continuous whistle rather than occasional, and doesn't matter whether a/c is engaged or not.

If it only happens when the a/c is on, I'm betting the source is the expansion valve, and the cause is low refrigerant charge. All my 124 cars became very talkative if the refrigerant was low. An expansion valve whistle cycles on and off, lasts for a few seconds, and is more likely to happen when accelerating because the engine is at higher RPM.

I suggest you check the refrigerant charge for starters. Might be an easy fix.

- JimY

gmercoleza · #8 10-21-2005, 10:35 AM

Hi jcyuhn, you may recall this is the car I worked on for a coworker a couple months back. Catastrophic compressor failure, so I replaced compressor, condensor, and receiver/dryer and thoroughly flushed everything else, then evacuated/charged properly. The guys at McCain's were a great help - thanks to you and Larry for the tip!

Anyway, this whistling was occurring both before and after I worked on the A/C and it's not related to the refrigerant charge. It is definitely coming from the HVAC center console area, and is definitely caused by changes in manifold vacuum. Specifically, it occurs momentarily when letting off the gas, no matter the speed of the vehicle (if my memory serves me correctly). It tapers and then disappears as manifold vacuum levels off. It is not a "constant" whistling.

I was just hoping someone here had seen this before and could offer some advice on where to look. The coworker is going out of town next weekend and is leaving the car with me, so I'm looking for ideas...

Anyone know where to get a MityVac cheap?

mpolli · #9 10-21-2005, 12:12 PM

I saw a TSB once about this. Said it was a clogged cabin filter.

Mike

jcyuhn · #10 10-21-2005, 01:23 PM

Yeah, I've seen the cabin filter TSB as well. Usually you get no air out of the vents as the first clue.

GM - I think you're on the right track with that car. If the whistle is tied to very strong manifold vacuum, I too think you're chasing a vacuum leak. Fortunately, I've never been under the dash of a 210, so I can't offer any advice. Make your friend buy you a mity-vac and go from there.

- JimY

f4iman78 · #11 10-21-2005, 11:02 PM

Sounds funny, but low refrigerent level will make a noise as you describe. Just a thought and maybe not your problem.Good luck.

3star · #12 10-22-2005, 02:12 PM

GM
I would be interested in knowing what you find.
Mine is definetely not due to partially open vents or clogged cabin filter.
It's a little different then your situation in that the squeak is not dependent on throttle. In fact it is heard best during idle when there are no other driving related noises. The squeak is very soft, intermittant, and almost appears to be a slow moving belt squeal/squeak and not really a whistle noise. Only when AC is on and not in EC mode.
Perhaps it is a low refrigerant charge, or vacuum leak as previously posted , which I can get checked next time I'm in for service.
Thanks

gmercoleza · #13 10-31-2005, 12:06 PM

UPDATE: I pulled the glove box along with the underdash panels and various shrouds and ducts, and was able to observe the motion of 3 visible HVAC actuator rods when the A/C is turned on. The whistling would start when one of the rods reached the end of its stroke. The culprit turned out to be the actuator pod connected to that particular rod. Removing it was one of the hardest things I have ever done - I think you're probably supposed to remove the dash when working on these things. It took me about 3 frustrating hours of contorting under and through the dash to locate and remove the faulty pod. Once removed, I turned the A/C on and the annoying whistling is gone.

Interestingly, the offending pod didn't seem to be moving its rod and corresponding lever through the full range of motion, probably due to the vacuum leak. So it seems that some function of the HVAC was not operating properly. But with the pod disconnected, I move the rod fully up and fully down, and can't tell any difference in vent output. Does anyone know what these 3 particular rod/lever/flap assemblies actually do? It almost seems like the defective pod isn't really essential. Perhaps it controlled the fresh air blend?

Sitting in my hand, the pod definitely has a leak and doesn't even hold vacuum very well. I took it apart to see if I could find a tear or crack somewhere in the diaphragm, but none could be found. It just looks like the parts no longer fit together well. The pod is made out of plastic, so I suppose some warpage is definitely possible.

By the way, I confirmed that it was the source of the loud whistle by encapsulating it in my hand with the A/C running, which resulted in the whistling being greatly muffled. Just thought I should point that out - when the whistling was occurring, due to the high pitch it was almost impossible to tell which direction it was coming from. At one point, I couldn't tell if it was coming from the pod or from the switchover box a few inches away. So muffling it helped me to be 100 percent certain.

Oh yeah, don't make the mistake of twisting the pod and disconnecting the rod from the lever at the top!!! It took me about 45 VERY frustrating minutes just to figure out how to reconnect it. I was practically in tears. I can't even imagine what I would have done if the lever broke!!!

Since I'm at work today, my wife is going to the dealer with the pod, in hopes of obtaining a replacement. Hopefully they sell these things or can order them. There was a blue sticker on it that appeared to have a barely discernable part number on it.

Once I have the new pod, I cringe at the thought of installing it. It will be painful and tedious. But I'm not doing this for free - my coworker will be paying me fairly, believe me... Can anyone tell me what a dealer or good indy would charge for something like this? It's not very technically difficult work, just very painful and time consuming. All in all, it will probably take me about 6 to 7 hours total. My friend will be thrilled - as great a car as it is, it was almost unbearable driving with that annoying whistling sound!

I'll report back to let everyone know how it goes...