AC whistle - PeachParts Mercedes-Benz Forum

JCE · #1 01-31-2001, 07:22 PM

After a freon leak got worse, I had the expansion valve and evaporator/dryer replaced, along with the "O" ring on the low pressure line at the firewall. The system was evacuated and converted to 134a at that time. The AC seems to work great, but since the conversion my blower makes a whistle. The pitch and volume of the whistle noise is dependent on the blower speed, and on whether or not the sun roof or window is cracked open. This occurs when the AC is in the normal settings of Auto fan speed, center button selected (Black arrow up, white arrow down) and fresh air switch set to fresh. If I switch to the dehumidify position (white arrows up and down), or switch to recirculate, the noise goes away. If I switch the fan to max, the noise gets worse. Any ideas about cause of the noise? Thanks for any help.

[Edited by JCE on 01-31-2001 at 07:26 PM]

jeffsr · #2 01-31-2001, 08:10 PM

I had the same problem, although not related to a conversion to R134. It was a partially stuck air door inside the heater box (plenum or what ever). The foam from one of the doors had come loose and was preventing the door from closing properly. Also varied with pressure inside the cabin. (windows up and down, more noise when down) What I did was let the engine idle (high mainfold vacuum), turn everything on and cycle all of the switches. Heat, AC the whole nine yards. Finally blew a chunk of this foamy stuff into the back of the center outlet. Problem solved. If this doesn't work, then you may have to get inside the heater box. Big pain in the a--. Hope for the best. Good luck..

JCE · #3 01-31-2001, 09:47 PM

Thank you, Jeffsr. I went out and tried that. I didn't get smacked in the face with any foam, but the whistle got a lot quieter, at least for now. Maybe I can borrow a fiberoptic Endoscope and go foam fishing!

MikeTangas · #4 02-01-2001, 01:08 AM

John,

I have a boroscope (sp) at my disposal. If you're passing up I-15 during day shift, we can take a look in your vents, see what's hiding down there. Maybe even take a looksie at your fuel strainer

.

Dr. Mike at your service.

JCE · #5 02-01-2001, 01:25 AM

That could work out well - what day and time work out for you? I never thought of using a borescope, but they certainly are more readily available than endoscopes.

MikeTangas · #6 02-01-2001, 01:45 AM

Let me check the schedules tomorrow, see what area(s) I'm assigned to cover on what days. I'm 99% certain that this Saturday at the I-15 facility would be good. Right now working Tues-Sat, next couple of weeks but the shooting season is rapidly approaching too, so Saturdays are going to be busy. Holding the Team try-outs on the 10th so that's a no go for a boro.

Been thinking about the best vent to access, either the right or centers should put us in the ball park (just don't know which will be closer). The scope has a light, but a narrow field of view, probably due to it's intended use, only needs a narrow view

. (probably talking about the same instrument just different terminology)

dtanesq · #7 02-01-2001, 02:03 AM

You only shoot on Saturdays? Is that wise; wouldn't it be best if no one actually knew which days were weapons free?

:-)

Sorry, couldn't resist....probably should've...

MikeTangas · #8 02-02-2001, 12:10 PM

Dan,

You seem to have forgot about all my brethren and sistren who cover the rest of the week

, kinda like playing the slots or lotto, you just gotta ask "do you feel lucky today? Well, do you...?".

John, I will be at the I-15 facility all day tomorrow. Anytime after the sun breaks over the mountain and warms the air a little should be good. Maybe between 10 am and noon, or 1 pm would be good. Should only take a few minutes to snake the scope in the vents and see what there is to see. Let me know.

JCE · #9 02-02-2001, 01:21 PM

Mike:

Those times sound good to me. I know how to get over the hill, but where is the I15 facility from there, (and is it on the north or south bound side-

duh!). Do I just drive up and ask for you? Will you videotape this as a training film on how to do a thorough vehicle search? I sure hope nobody at the factory left a small bag of white powdered dessicant in the vent ducts - that would probably ruin the whole weekend for me!!!

MikeTangas · #10 02-02-2001, 06:50 PM

John,

If you come across the Ortega, go south on I-15 to the San Diego County line. Exit at Rainbow Valley, cross over the interstate and come back north 1 mile. Stay in the #4 lane (the right hand lane) and tell the first smiling person you see you are looking for me. Yes the area is under video surveillance and taped, but we'll try to get out of the field of view. While we're doing this I can relate a 300D story to you.

See you manana.

JCE · #11 02-03-2001, 07:44 PM

In the midst of his Suburban troubles, Mike took the time to run a borescope 3 feet into the dash vents of my car to identify the whistle. Looking through the scope we were able to see the inside of the ducts, and a vacuum operated door that opened and closed with the switches on the dash: AC in normal mode (black arrow up, whiter arrow down button), door closed and whistling; AC in "EC" or dehumidify mode (EC button or 2 white arrows button), door open and no whistle. We could see that most of the foam around the door was gone, but a small section was still intact. We went in 3 feet from the passenger dash vent. Is there another door 3 feet in from the drivers vent? The bore scope trick is real neat, but it is hard to tell the position of things you are looking at inside the duct.

Question for the group - is the door whistling because the small chunk of intact foam is preventing a tight seal, or does the door whistle because the foam is needed to prevent air leaks that whistle. Jeffsr: did the whistling go away after the foam was all cleared out, or did you have to replace the foam?

Also, behind the door there was what appeared to be a thin blue (UV?) light. It was a real light as far as we could tell, not a reflection off the scope light. Were we seeing a section of the sky through the defrost vent, or does MB put an anti-mold light in the plenum??? Like I say, it is real hard to determine direction with the scope.

Thank you Mike, Jeff, and everyone else on this forum for all the help, and for any answers to these puzzles!

MikeTangas · #12 02-04-2001, 02:55 AM

As for the light John mentioned, due to it's color, I was reminded of the ozone lights that used to be mounted in clothes driers.

Also, due to the scopes bending through the ductwork, it is hard to get a perspective of how things are laid out. I'm guessing the door's positions are parallel to the firewall and perpendicular to the firewall ( _ & l). The whistle occurs when the door is perpendicular to the firewall (recirculate?). If only the scope had a grasping claw on the end of it, we could have plucked the remaining foam particles from the edges of the door.

Now one thing John forgot to mention was how clean his ductwork was. I watched the entire length of the ductwork and it was absolutely immaculate, no dirt, dust, hair balls or foreign objects.

JCE · #13 02-04-2001, 01:34 PM

You wouldn't believe how difficult it is to clean out those ducts with Vinylex and a toothbrush every weekend

!

MikeTangas · #14 02-05-2001, 12:15 PM

for the cookies. I did share a few with my cohorts and the kids too. They loved them.

(just trying to keep this at the top, gotta know about that light!!!)

JCE · #15 02-06-2001, 02:10 PM

Any ideas on the blue light in the AC system? (No, we didn't use a K-mart 134 conversion kit, so that isn't it

)

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