mold doesnt seem to be the issue.
as for the coolant leaks i'll check the level, though i have to say that i havent smelled any coolant inside the vehicle at all...
I'm driving the car with the CO detector inside and so far the readings are coming out to be normal...

Headaches
 

Coolant could very well be outgassing from a simple small leak that has not developed into a noticable leak yet (dampness around a hose fitting) so don't rule this one out yet. You could try to disconnect the heater hose from the aux. water pump and ride without the heat (using a 12v electrical heater) to confirm or deny this as the culprit.

This case reminds me of the Army brass at Ft. Benning that had his engine replaced in his Cadilac. When he got the car back, he started to smell a foul odor, and couldn't find the cause. Since he car-pooled (and drove his Caddy) each morning he would have a car load riding to the base with the windows down, and it was winter time (cold, but in Georgia). His wife told him to sell it or she would not ride in it anymore.

He took it to a car wash and they removed the back seat looking for the cause, and found a dead mouse that had crwaled into the car and died while having the engine replaced in the shop. The Caddy had leather interior, which is pourous, so the stink was aweful, even after two trips to the car wash at $200! I could hardly stand smelling it before I placed my air purifier in it, and the windows had been down all day! So, the army brass told me that if my machine worked, he would buy one for his home. It worked, but he didn't make a purchase, because the problem was gone.....that's how the government works sometimes, huh?

Hope you locate your source of headaches. It seems to be air related.

I'll look for small leaks of coolant again. My only question is... wouldn't I smell the coolant if it's fumes were entering the cabin causing a headache ? I'm assuming the fumes would carry the coolant odor as well... the car is using the green stuff, not the original mercedes coolant. And I can certainly tell the smell of the green coolant

Maybe the smell is so slight that you are used to it. Have somebody who hasn't been in the car for awhile ride in it and see if they smell anything. Coolent you should smell. Leaks should be easy to spot. Gunk the engine and clean it real well to remove coolent any that may have been spilled. Good luck.

Is the A/C system still charged? Maybe it is R134 or R12 slowly leaking out and into the vents. Long shot.

This is a serious problem so be careful and drive with your window open unitl it is solved. I think you are on the right track with the CO from the exhaust. I've had coolant leaks that you definately can smell and I don't recall getting a headache. The detector is a good first step but it may not be sensitive enough to trigger the alarm.

Is there any way to have someone (midas, carx, etc..) pressurize the exhaust system all the way through the exhaust manifold and check for leaks. I would think that this has been done before.

If the exhaust is OK maybe there is a dead cat in your air intake.

Headache
 

Either way, coolant off-gassing would be hard to smell, unless you had the nose of a k-9. Small amounts of coolant off-gassing could not be detected by your sense of smell, while causing a headache.

The problem seems to be related within the air stream, and if it is not coolant, refrigerant or any other off-gassing, the only other thing I could think of is ionization. Positive ionization causes headaches, and they are termed "ill winds", and in some parts of the desert in the Middle East, the suicide rate is incredible when positive ionization is found in abundance. If you have an electrical component that is somehow spraying positive ionization into the air stream, this could possibly cause the headaches. I know it may be difficult to determine, but if you take a look around in the dark with the engine running, you may find some sparks or signs of a switch or other electrical component showing signs of failure.

Negative ionization removes the headache, and actually stimulates the central nervous system, and is used in hospital to treat burn patients, since it promotes skin healing at an advanced rate.

This is just something to consider, so if you don't locate any leaks, it may be positive ionization in the air stream. Have you confirmed or denied the coolant issue with disconnecting the heater hose connection from the engine yet? It is worth a shot.

Hope you discover the issue, and when you do, please let all of us know. I know what I make mention of here is a long shot, but since you're still fishing for the cause, I thought to let you know of what I had in mind, since I have studied ionization extensively over the past 13 years. It is a mind opening experience to discover what your indoor environment can hold for you. Even mold, in the early stages is not detected by your sence of smell, and can cause severe headaches and black lung disease.

Hey, I just thought of a way to confirm or deny if it's air-stream related. If you have access to an expensice resperator that would protect from carbon monoxide and other gasses, try wearing it while driving, although I would do this test at night when no one could see what you are doing :D.

Also, have you conducted a search in your interior? Like removing the back seat, looking under the front seats, glove box and elsewhere? Even spilled liquids that have dried (such as dry-cleaning fluids) can still out-gass and cause headaches. I am very sensitive to those cleaning agents. Even some bar soaps cause me a minor skin irration.....(Ivory has been the best for me :))

Hope this helps.

dtf,
you bring on an interesting point. the r12 was infact leaking because my car was in for service just last week to have the compressor changed. They changed it after they found that the R12 was leaking. that however has been fixed at this point.
I've been driving the car for two days now ever since it came back from the dealer for the r12 leak fix. The CO detector is giving out normal readings. I've placed the CO sensor at various locations to make sure I dont leave any spot inside the car.
It's been raining here in NJ all past week so I can't really open to hood to find out coolant leaks since it'll be hard to spot them in such heavy rain :)
I will keep you guys posted.
thanks again for everyone's posts and helpful hints.
happy new year to everyone.

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 tried to smell the antifreeze but couldn't. the coolant level is perfect as well.
Here are the questions :
with the heater on, are all the vents for cold air closed or is the fresh air mixed with the heated air and then blown in through the vents ?
secondly, what's the path that the hot air takes starting from the front of the car all the way into the vents... because obviously somewhere along that path is where the problem lies...
I'll wait for everyone's replies..
thanks !

Still Online?
 

If you are still online, I just sent you a PM.....need your email address to send you some PDF files.....and which car are you working on again?

ok guys,
I'm not sure the two problems are related or not. but my vacuum actuators are acting up meaning i'm having problems with heat / cold climate controls. I had posted that issue right before the car went in for the service of A/C freon etc.
The dealer has told me that I'll have to replace the vacuum actuators, all six and quoted 9 hours just for labor. ahem !
the question is, does that somehow translate into fresh air not being able to be supplied to the cabin while the heat is on, resulting in loss of fresh air ( thats if there is such a concept of fresh air coming in as well while heat is on) and resulting in headaches due to lack of fresh air ?
the reason i ask is because with the heater off, and the vents on just for cold air there are no headaches.
the center vents aren't working while on the cold temp setting but then again that I know is because of the vacuum actuators....
any ideas ?

Excess CO2 will cause headaches too I think. Maybe you aren't getting fresh air like you're suggesting or even maybe the recirculating part of the climate control is stuck on 'cabin' not allowing fresh air in. I am not familair with the vaccuum actuators or their mechanics. Sounds like you are getting close though.

I was searching through the posts and came up with a lot of posts where the center vents stopped working in the heating system. However I didn't read any of the posts complaining of headaches while the vents were not working properly.
can someone shed some light on this ?
thanks.

I'm only familiar with the heating system on a 123 so take my ideas with a grain of salt. In a 123, a vacuum actuator permits fresh air to enter. I don't know the exact relationship to the center vents but it seems to me quite possible that if the actuator for the vents is bad, the actuator for the fresh air could be bad also. The way to tell is to identify it, and pull a vacuum on it.

when the heater is ON, does all the air coming into the cabin travel through the heater core, or is there another vent that lets the air in through another channel at the same time ?