: Odd problem with my car...maybe you could help?



I~LUV~Caddys8792
01-01-08, 10:38 PM
This is kinda complicated, and it's not a Cadillac, so bear with me a second please. I know that we've got a lot of great minds on this site that know a lot about the inner workings of these things, whether or not it's a Cadillac, so that's why I'm posting it here, along with MBworld.


First I gotta say that It seems as though that right after I had my headgasket replaced, this started happening, and I took it to the dealer shortly afterwords, and they found that this wasn't caused by any of their work, but I have my doubts.

Anywho, the problem is that when it's below approximately 15* outside, the HVAC system will default all the air through my defrost vents when I give it any throttle, until the car thoroughly reaches operating temperature, then it works fine, even at WOT. But for those first 10-15 minutes, it's wierd. And if I let it sit for a while, and get back in it, it works fine, but it seems it'll only act up when I first start it up in the morning...so basically it only happens if it sits for like 6+ hours.

The first thing that came to mind was that I was getting ice in a vacuum line or a check valve, and that's why it defaults to Defrost only when it's very cold, but after it reaches operating temp (and thaws out) it works fine, so I told them that when I went into the dealer a few weeks ago, and they looked it over, checked for any errors on their part, and they didn't find any thing that they could have caused, so they're thinking that it was a problem with that "vacuum box" (for lack of a better word, it's in the dashboard, and it takes the vacuum line that runs from the engine, and diverts it to operate all of the blend doors). And obviously, it wasn't caused by the HG repair...it's just a tremendous coincidence.

So now I've gotta go back there, if I decide to look into this any further, pay for the one hour of diagnosis, figure out what it exactly is, and if I'm lucky, the warranty company will cover it. Otherwise, I'll be out the $115 for the diag, plus the repair costs if I wanna pay out of pocket for it, or I could just live with it and wait until I've got more money to deal with it.

dkozloski
01-01-08, 10:42 PM
Somebody swapped some vacuum hoses around. It's going to be a maintenance failure.

AMGoff
01-01-08, 11:30 PM
Well.. in those overly-complex systems MB uses... I do know whenever there is a system failure, whether it be something with the vacuum or electrical, the system will automatically default to defrost. It could be something as simple as a solenoid... but Lord knows with those things.

That's one thing I'll never understand about Mercedes (although it's not like other luxury manufacturers aren't guilty of it as well), why the hell must they make everything so damned complicated? There is absolutely no reason why they should have built the climate control system of that car to me more complex then then entire electrical systems of some "regular" cars. That's why technological doodads and whatnot are all fine and dandy - only when they're working.

Anyway... is this something that really, really bothers you? If not, I'd just let it go for a while, save up some money, and tackle it sometime before next winter. Just keep an eye on it to make sure it doesn't get any worse... if it does and it defaults to the defrost all of the time then you're pretty much assured to have a total system failure and then you'd definitely want it taken care of. Either way they're going to have to tear into your dash, firewall, and engine bay just to find what ever it is.

The only other possible thing I can think of would be if your car overheated? Which I'm not sure it did or not.... if it did, you very well could have developed an air lock in your cooling system... which could have something to do with it all... but again, I can't remember if it did or not.

I~LUV~Caddys8792
01-02-08, 12:38 PM
Well darn it, that's not good news. I guess I'll just have to live with it until I can scrounge up some money to take it into the dealer. For now, I guess I'll just enjoy getting a blast of warm air to the face whenever I step on the throttle. And no, it's never overheated.

firstimecaddi
01-02-08, 12:56 PM
@ILUVCADDY who's the chic in the pic!

I~LUV~Caddys8792
01-02-08, 12:56 PM
Fiona Apple.

firstimecaddi
01-02-08, 12:59 PM
cool...is she a performer/actor???

I~LUV~Caddys8792
01-02-08, 01:07 PM
She was a pretty famous singer about 10 years ago. Best known for her song "Criminal", which is where I get my tagline "I've been a bad, bad girl". Check her out.

RightTurn
01-02-08, 01:12 PM
Solution: Ditch the Mercedes and buy a Caddy. :D

hueterm
01-02-08, 01:24 PM
And the defaulting to defrost thing isn't a "safety" override until the car warms up?

I remember on some car I had (either the '92 Toro or the '99 GP), the heat wouldn't come out of the floor until the car "warmed up", but you could use the defroster.

I~LUV~Caddys8792
01-02-08, 01:32 PM
Solution: Ditch the Mercedes and buy a Caddy. :D

LOL.....not quite yet. I'm not ready to throw in the towel yet, but if I ever do, and decide to get into a Cadillac again, I'll be looking for a real late model ETC or '01-03 STS.


And the defaulting to defrost thing isn't a "safety" override until the car warms up?

I don't think so...I mean it only does it when it's below about 15* outside, and only when I'm giving it throttle, whether it be 10% throttle, or 100%.
And after about 15-20 minutes, it acts completely normal.

hueterm
01-02-08, 01:38 PM
That is weird...

So when you don't give it throttle, does it just blow no air, or does it come out of the floor?

I don't know that I'd rip the dash apart just to fix that -- IF you have floor heat after a few minutes. Who knows what would get screwed up if they take the dash apart.

Or -- something else could break in the meantime (sorry to be so pessimistic)and then they could fix them both.

I~LUV~Caddys8792
01-02-08, 01:40 PM
That is weird...
So when you don't give it throttle, does it just blow no air, or does it come out of the floor?

When I don't give it any throttle, it'll blow the air out of the floor and defrost, which is normal, but when I give it throttle, it'll divert all the airflow to the defrost vents.

Cadillacboy
01-02-08, 06:41 PM
Another peculiar problem w/ W140s
:doh:

Don't let this bring you down , you still have a cool MB . At least you don't have wiring harness culprits lol

caddycruiser
01-02-08, 11:00 PM
LOL.....not quite yet. I'm not ready to throw in the towel yet, but if I ever do, and decide to get into a Cadillac again, I'll be looking for a real late model ETC or '01-03 STS.


Dear lord NO...don't ever do that. Well, at least not if it also means getting rid of the Benz. No offense to people with them...but, ugh...just IMHO.

That said, where's our in-house MB tech? He could probably give details on this, and know what it is. Can't be that complicated of an issue. And, actually, doesn't sound any weirder than some things that have popped up, mysteriously, with our Roadmaster & Fleetwoods. Cars are machines, to varying degrees of complexity, and things happen.

It really does sound like some kind of an oddball vacuum line or small sensor/switch somewhere...the dilemma is narrowing that down among a thousand things.

I~LUV~Caddys8792
01-03-08, 12:03 AM
It's gotta be vacuum related....why else would it only do it when I'm applying throttle?

PAGING CLARK Z71 or DANBUC!

Destroyer
01-03-08, 12:07 AM
LOL.....not quite yet. I'm not ready to throw in the towel yet, but if I ever do, and decide to get into a Cadillac again, I'll be looking for a real late model ETC or '01-03 STS. Yuck! :vomit:

I~LUV~Caddys8792
01-03-08, 12:25 AM
Well, good news.
Using the Mitchell Mercedes-Benz CD rom manual I got from my uncle for X-Mas, I was able to find out that the vacuum check valve is not located in the engine compartment, like on most cars, but it is attached to the main "vacuum box", located under the dashboard.

This is good news, because my father and I have been pondering this for a while, and we've led to believe that the check valve has some sort of moisture in it, and it freezes up when it gets real cold out, which would explain why it only happens when it's below 10* out, and the car has been sitting for all night. Our problem was we didn't know where said check valve was located. Now we do. Now just to access it....