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Benz300, Just another thought. The vent system in these cars goes out througt the trunk. If there is no fresh air coming in the front through the vents. the exit vents may drawing exhaust in. These vents have a flap so air should only go out. Just a thought. Norm in FL

Norm

I think that is a great point. Also I have noticed these flaps get old and just don't work the way they were designed to.

Haasman

Quote:

Benz300 wrote:
allright here are some updates....I went for a long drive tonight to figure out what exactly is going on. the CO detector showed normal readings through out the drive. here's what I found. the cause of the headache is the heat.. not the vents or the air from outside. with the temp to the heating level, it feels as if someone has sucked the fresh air out all together and I need to open up the windows to breathe. but when I turn the knob to cold temp everything is perfectly fine. I tried it with both on the e/c mode and also with the A/C on in both hot and cold levels. same thing. when the hot air blows through the vents it brings along headache... I'll wait for everyone's replies..
thanks !

Seems like you have figured out the cause, but have you thought of the solution? Heat temp. too high? What is your highest heat temp. while going for a long drive?

A thought triggered by the cabin-vent-flap post: What happens on AC when you hit the recirc button?
I'm still looking at exhaust as the most likely culprit, given the known characteristics of CO. Have had a coolant leak into the heater core, and in that particular case there was not only a noticeable odor, but a film developing on the inside glass ('99 Saab in a Michigan winter).

Well,
there's no odor even the slightest inside the cabin that would indicate the coolant leak. however possbile. But as indicated by some other posts there's no sign of a film buildup on the windscreen either. I double checked.
the heat that I kept the car on was at 70 to 75 just when the flaps flip and the heater kicked in. nothing too high at all.
as for the exhaust coming in, are we suggesting that the ventilation is proper when the temp is set at cold and as soon as the temp control is set to high, the heater kicks in the ventilation becomes all tangled up letting the exhaust fumes from the trunk inside the cabin somehow ?
THe reason I'm stuck with doing this myself is because the dealer is dumbfounded. their only suggestion was they want to throw a 1500 bill towards me to fix the vacuum actuators first and then look at something else. which is ridiculous because after fixing all that if they say they have to tackle the heater core they'll charge me for another 18 hours of labor to open the whole damn dash again. And i'm not ready to spend another 4K on a car that i've already spent almost 7K on. and at the end the car's resale value will never exceed 5500 to begin with.

Vacuum actuators

Hi there, just a thought, get your hands on a vacuum line diagram showing the complete vacuum schematic relating to the climate control system.

Trace (check for) vacuum present starting at the source, then step by step through the system.

Your problem could be as simple as a vacuum leak or faulty vacuum switchover valve.

Acky