Hi Scotty, I have a real tough one for you. I have a 2017 Cadillac XTS 3.6L V6 AWD with 195,433 miles on it. (HAD 65,000 when purchased)

Everytime I turn on the Heat or A/C I get an irritated throat which causes a dry cough sometimes and it also irritates my eyes. There's also a slight burning sensation around my lips, eyes, nose and a slight burning taste in the mouth.

I've been trying to research it and can't find anything online with the exception where a woman had some work done to her car and what she described was the same thing I'm experiencing and no one including shops she took it to could figure out what it was. She eventually sold the car & never found out.

This baffles me because, I've been a mechanic for many years and had never came across anything like it. I was even an Electrical Systems Engineer at Ford and although I don't know everything about a car, I know a lot. I don't suspect antifreeze (no leaks) & no wet floor from heater core etc... plus I think the smell would be more pronounced and there would be a sweet smell in the vehicle. This is more like a chemical or burning sensation like after eating hot sauce around the lip area and irritation as you breathe in the nostrils as well as the irritated throat.

I was suspecting the refrigerant used in the cooling system but from what I understand it doesn't irritate like that and is usually harmless. I did buy this vehicle used and didn't have this problem until I ran over a thick patch of snow & ice that pushed my exhaust system back slightly cracking the weld on the front Catalytic convertor where it mounts to the block. I thought that was the issue at first. However, I replaced it and checked the rest of the system for leaks and haven't found any but after that happened is when this started happening.

I spent the winter checking and rechecked the exhaust system so many times because it was so bad. Of course when summer came around and I had to use the a/c I still have the same problem. I've also changed the cabin air filter. The antifreeze has never got low and I haven't seen or detected leaks so I don't suspect that. The a/c works fine. I've been using it all summer and it does get cold (sometimes too cold) although there was maybe once it struggled for a couple of minutes but it was almost 100 degrees out and managed to get cold once I started driving. Now I haven't checked the a/c system for leaks because of that.

Also I don't see anything else leaking anywhere and besides we know what oil, trans fluid, power steering fluid etc... smells like and none of those I'm smelling and it's not a "smell" anyway. It's more like an irritation to the mouth,, nose and throat.. I am really baffled by this and I really need to fix it. I can tell it affects passengers as well because they will clear their throats,, cough and even sneeze sometimes. I don't want to take the whole dash apart just to check for leaks in the housing either. That's a lot of work to find no leak. I did remove the blower motor and ran a flexible camera into the housing looking for any leaks and didn't see anything alarming but admittedly I couldn't see every single place in there and it was a cheap camera.

What do you think? Any opinions? Maybe you may want to take this on as a challenge or make a video about it....