I get a vaguely nauseous/ "not fresh air" smell coming from my HVAC. I think it's more heat associated than with the AC, which makes me think that the outside of the heater matrix might need a rinse. I redid the o rings in the summer, but was on AC for months, and only recently started to require heat. It was quite unpleasant at first, and is becoming less noticeable now. I have no reason to think the matrix is leaking. I'm not too hot on the HVAC anatomy, but does anyone know of any good ways to clean the outside of the matrix? There are various "bombs" available on the market - anyone found a good one? If i wanted to do a more physical clean is that going to be a dash-off job, or is there a pathway to getting an aerosol solvent directly into the heater box via one of the vents?