Center A/C Heater Vent problem

[htfan1]

My center A/C & Heater vent started malfunctioning around the same time I started noticing excessive vacuum pump noise. (I think I have vacuum leak).

Some time the air will flow through it fine and some time it doesn't without any changes to the vent controls. (I believe the vents are vacuum controlled.)

How should I start looking into this?

[djdoughboy]

i dont think it has anything to do with the vacum pump... i think your problem may lie in the blower regulator... or the blower motor itself... but most likely the regulator... it is fairly easy to get at...

click here for instructions on how to remove the blower motor (http://mbclub.co.uk/forums/showthread.php?t=3593)


now when you remove it you will see that the regulator is on the blower motor where the power wires connect to it... this is probably your culprit... (in the above how-to i believe they refer to the regulator as the speed controller)...

or it may be that the fan itself needs to be oiled a little... sometimes this is the problem... you can power the fan motor directly with 12v to see if it is working properly... and see if it needs to be oiled... if it seems to be working well most likely it is the regulator...



Sean

[htfan1]

Originally posted by djdoughboy
i dont think it has anything to do with the vacum pump... i think your problem may lie in the blower regulator... or the blower motor itself... but most likely the regulator... it is fairly easy to get at...

click here for instructions on how to remove the blower motor (http://mbclub.co.uk/forums/showthread.php?t=3593)


now when you remove it you will see that the regulator is on the blower motor where the power wires connect to it... this is probably your culprit... (in the above how-to i believe they refer to the regulator as the speed controller)...

or it may be that the fan itself needs to be oiled a little... sometimes this is the problem... you can power the fan motor directly with 12v to see if it is working properly... and see if it needs to be oiled... if it seems to be working well most likely it is the regulator...



Sean

Thank you! Great information.

However, the blower seems to be fine. At times when the center vent doesn't flow, the side dash vents dramatically increase in flow to compensate for the blocked center vent. In addition, if I select a floor or defrost setting the flow is great through those openings.

The problem only occurs when I select flow through the dash vents only.

I think it could be related to the center vent open/close control. Isn't that vacuum controlled?

[djdoughboy]

ahhhh i see... yes i think you are correct... vacum controled... now that i hear that... i would wager that it DOES have something to do with the vacum pump hahaha... sorry to mislead you with the first advice...



you probably have a vacum leak or maybe the vacum pump is bad... if you have a pre-updated car then it is in the engine bay... if you have an updated model it is in the trunk...




Sean

[Josh R]

Under the passenger side of the dash, (remove the bolster cover) you will see the vacuum diaphram switching unit. Its small black and has alot of plastic vacuum lines going to it. Remove the bolt I believe its a #20 torx, Open the unit, be carefull though. Now all the vacuum lines except for 2 of them operate the diaphrams that are attached to the heater box. Use a vacuum pump and test each vacuum line independently to see if it holsa vacuum. They should hold vacuum. If one doesn't you will need to replace that diaphram. 90% of the time its the center vent diaphram that goes bad, in order to fix the problem dash removal is required. Typical time to fix complaint is 8 hours. Also in the engine compartment on the passenger side near the DME is a black vacuum switching unit with green,yellow,grey,and black vacuum lines attached to it. At the end of this switching unit look at the ball bearing that is used to seal the vacuum, sometimes it will crack and cause a vacuum leak. This switching unit is what supplies vacuum to the interior switching unit located in the passenger compartment. Start here first. Hope this helps.

[djdoughboy]

good info...






Sean

[htfan1]

Yes, great info!

Thank you Josh.

The 8 hours concerns me a little. Do you know of any good shops in the LA/OC area that can do this work for reasonable $$?

[Josh R]

Try Johnson Motorcars in the city of Orange. Talk to Gary Johnson.

[htfan1]

Originally posted by Josh R
Try Johnson Motorcars in the city of Orange. Talk to Gary Johnson.

Thanks! I'll give them a call.

[benzdude280]

Could this also be a problem with the bivalve? Just wondering.

[htfan1]

Originally posted by benzdude280
Could this also be a problem with the bivalve? Just wondering.

How would I check this?

[benzdude280]

When mine went out, there was cold air coming out the side vents and hot air coming out the center vents. Otherwise, I wouldn't know any other way of checking it. Sorry for the lack of info. Anyone else out there know?

[htfan1]

Originally posted by benzdude280
When mine went out, there was cold air coming out the side vents and hot air coming out the center vents. Otherwise, I wouldn't know any other way of checking it. Sorry for the lack of info. Anyone else out there know?

Thanks for the info. Actually, you gave me enough information to rule out the bivalve.

My center vents have no flow at all when the problem occurs.

[Sulaco]

Wow. I am having this exact same problem. I've had it for quite a long while now (more than a year?) But never noticed it until this summer came along and I needed those center vents to blow lots of cold air. I'll crank the car, take off down the road with all the dash vents blowing full speed, then a few minutes later the center vents slowly cut out, and all of their air is redirected to the side dash vents and the windshield defrost vent. Sometimes I can kill the car and crank it again and it will fix it. Other times, nothing will fix it. And in this humid 96F TN heat, it gets REALLY old. Fast.

Edit:

I can hear a vacuum leak on that switching unit underneath the hood. Upon closer inspection, the plastic around the ball bearing is cracked. So that's probably what's causing my problem? How do I get that sucker unplugged and out of the car to replace it?

[Sulaco]

I replaced the plastic vacuum junction/switch under the hood that was cracked. Now my center vents never work.

Hooray for motherfucking engineering greatness!

Also, half the time I leave from a complete stop I get booted into Limp mode, and EVERYTIME I re-accelerate after slowing down I get booted into limp mode.

Not happy.

[Rocky]

For guys with the problem of different temps between the center vents and outside vent's it's the duovalve (monovalve, it has different names). It's located in the engine compartment by the firewall on the passanger side. It looks like 2 'C' batteries beside each other with 2 tubes that go intot he firewall if I can remember right. This piece has diaphrams that individually control the side vents and the center vents (hence duo valve). This is on a W202.

[Rocky]

Originally posted by htfan1
My center A/C & Heater vent started malfunctioning around the same time I started noticing excessive vacuum pump noise. (I think I have vacuum leak).

Some time the air will flow through it fine and some time it doesn't without any changes to the vent controls. (I believe the vents are vacuum controlled.)

How should I start looking into this?

I had the same problem. Fixed now since I totaled the car almost a year ago hahaha.

Sorry, I didn't end fixing it.

[htfan1]

Originally posted by Rocky
I had the same problem. Fixed now since I totaled the car almost a year ago hahaha.

Sorry, I didn't end fixing it.

Well ... that's one way to solve the problem! (I haven't fixed mine yet.)

I've had a couple shops look at it and give me similar opinions usually including numerious $$$$ as part of the conversation.

I'm kinda starting the get used to the WRRRing noise from the pump. It's normally stops after a few minutes of driving. However, I know I'll need to get it fixed sooner than later. I'm sure extra wear on the pump is not good.

I look at the bright side... It a good conversation piece! People get in my car and ask "WHAT THE HECK IS THAT NOISE!"

Then the story begins...

[loudandheard]

I just noticed when I put on my heater the hot air only blows out of the side vents. When I put on the ac it mainly blows through the center vents. I haven't heard any vacuum leaks, I just thought that's how it was suppose to be.

[htfan1]

Originally posted by loudandheard
I just noticed when I put on my heater the hot air only blows out of the side vents. When I put on the ac it mainly blows through the center vents. I haven't heard any vacuum leaks, I just thought that's how it was suppose to be.

My vent problem doesn't seem to care if it's hot or cold, A/C or heat.

However, it is consistently random....

[Sulaco]

Yeah, the heat won't blow out the center vents unless you specifically order it to do so via the controls. Plus, most A/C does come through the center vents (back when they worked).

Dude, my vacuum pump has been buzzing like that for years. I'd say going on 3 whole years now. I've fixed every vacuum leak I could find and nothing helps. I've just given up. I've just given up on alot of things on my piece of shit lemon. I've got a 50/50 chance of it dying on me when I try to pull out in dangerous traffic situations. I'm afraid of getting hurt when it is inevitably t-boned in traffic due to whatever the fuck is wrong with it--and if it weren't for that fear, I would gladly wreck the fuck out of it. And yes, it works VERY well as a conversation piece.

"WTF"
"Vacuum pump."
"WTF"
"It uses a vacuum pump to control all sorts of things like door locks, A/C controls, etc."
"WTF"
"It has a vacuum leak somewhere."
"WTF FIX IT"
"The tiny plastic piece that is causing it costs more than the car is worth."
"Oh."

[Rocky]

Originally posted by Sulaco
Yeah, the heat won't blow out the center vents unless you specifically order it to do so via the controls. Plus, most A/C does come through the center vents (back when they worked).

Dude, my vacuum pump has been buzzing like that for years. I'd say going on 3 whole years now. I've fixed every vacuum leak I could find and nothing helps. I've just given up. I've just given up on alot of things on my piece of shit lemon. I've got a 50/50 chance of it dying on me when I try to pull out in dangerous traffic situations. I'm afraid of getting hurt when it is inevitably t-boned in traffic due to whatever the fuck is wrong with it--and if it weren't for that fear, I would gladly wreck the fuck out of it. And yes, it works VERY well as a conversation piece.

"WTF"
"Vacuum pump."
"WTF"
"It uses a vacuum pump to control all sorts of things like door locks, A/C controls, etc."
"WTF"
"It has a vacuum leak somewhere."
"WTF FIX IT"
"The tiny plastic piece that is causing it costs more than the car is worth."
"Oh."

I would pull the CEL codes even though the CEL light is not on. Maybe your CEL light bulb is borked? Or someone put a piece of black tape over the light becuse they can't bother trying to fix the car and have an oprange light stare them in the face.

[Sulaco]

CEL not on, bulb isn't broken, I've had the instrument cluster out of the car and personally inspected it (making sure my perpetual SRS light that was no longer on died because of a bulb. of COURSE the SRS system isn't working right. it MUST be a dead bulb). No codes being sent (had it scanned several times thinking it was sending codes but not setting CEL on).

[htfan1]

Originally posted by Rocky
I would pull the CEL codes even though the CEL light is not on. Maybe your CEL light bulb is borked? Or someone put a piece of black tape over the light becuse they can't bother trying to fix the car and have an oprange light stare them in the face.

In my situation, I've checked for CEL codes. There are none to pull. I'm afraid the CEL light works fine.

[htfan1]

Originally posted by Sulaco
CEL not on, bulb isn't broken, I've had the instrument cluster out of the car and personally inspected it (making sure my perpetual SRS light that was no longer on died because of a bulb. of COURSE the SRS system isn't working right. it MUST be a dead bulb). No codes being sent (had it scanned several times thinking it was sending codes but not setting CEL on).

I had posted a similar SRS issue some time back. My SRS light was on so long it killed my bulb too. Luckily, the dealer had an instrument cluster recall and replaced the whole thing for free. However, then the RED SRS light was back!

Dealer said the main SRS was bad and wanted around $800 to fix. I replaced the main air bag sensor/computer myself with a salvage part I purchased, had a local MB shop test and reset the system. The SRS system is working fine now.

[Sulaco]

I'm afraid I have no options left on any of my issues. I don't have a single dime to spare (I'm in college, afterall). Looks like I'm better off setting it on fire and praying the insurance company gives me more than 2 or 3 grand for it.

[htfan1]

Originally posted by Sulaco
I'm afraid I have no options left on any of my issues. I don't have a single dime to spare (I'm in college, afterall). Looks like I'm better off setting it on fire and praying the insurance company gives me more than 2 or 3 grand for it.

I know where you're coming from! I've been there before. Believe me, it will get MUCH better after college!

[Sulaco]

I don't know, I'm already 24,000 in debt for college. The car has been paid for since I got it, but I still consider myself "in debt" over it (it's a flaming piece of shit in need of so much repair.)

I think first gear is starting to slip. Again. Another $1384 soon. Yay.

[htfan1]

Originally posted by Sulaco
I don't know, I'm already 24,000 in debt for college. The car has been paid for since I got it, but I still consider myself "in debt" over it (it's a flaming piece of shit in need of so much repair.)

I think first gear is starting to slip. Again. Another $1384 soon. Yay.

Don't loose site of your goal! I can't remember the details of the salary stats for college grads compared to non-college. However, once you graduate and start working the college degree will pay for itself fairly quick. Then it just gets better.

I was flat broke in college too.

[Sulaco]

Well, on the bright side I got the violent vibration in my brakes fixed. New rotors and pads all around!

Only now it can't go well enough to really notice the brakes, and with barely functioning A/C I never want to drive it.

[Sulaco]

Originally posted by Sulaco
Well, on the bright side I got the violent vibration in my brakes fixed. New rotors and pads all around!

Only now it can't go well enough to really notice the brakes, and with barely functioning A/C I never want to drive it.

Common occurence here (I live with 30 friends in a big house):
"Hey, Carroll! You drive, you're the one with the Benz!"
"A/C barely works and I'll need to stop and re-start it at least 5 times on this 3 mile trip."
"Oh, fuck. Well, we'll take my Jeep then."

Embarassing.

[crit1]

I'm having the same problem. Is there a way to replace the vacuum switching unit without taking out the dash? If the dash has to be removed, does anyone have instructions to remove it?

[htfan1]

Originally posted by crit1
I'm having the same problem. Is there a way to replace the vacuum switching unit without taking out the dash? If the dash has to be removed, does anyone have instructions to remove it?

Yes, you can get to it from below the dash without actually removing the dash. I believe there is a posting with instructions so do a search on the forum.