When the car first started, I used to get a smell of leather mixed in with a soft, warm faint smell of engine components (the smell most cars give off when first started) but now when I start the car with the A/C, it smells faintly like mustard(?) and the smell of oil (engine components) is a little stronger. It performs normally, it's just that the smell changed all of a sudden. What might cause that? It is a 2001 Audi A4 2.8 Quattro with 87,000 miles.

 

Remove the cabin filter. Spray Lysol into opening with the vent. fan on.

 

The problem is caused by mold growing in the moist environment from the condensed water that's in the air.

I found a professional cleaning kit from "Certified A/C PRO" called Evaporator Odor Eliminator. I found it for $9.00 at NAPA Autoparts..

The kit comes with a hose that you're supposed to attach to the drain. That's a real pain to do in the Audi. I just snaked the line into the right vent in the center console until it hit resistance. Then followed the directions from there.

Note, that it will drain right out through the drain hose. So, make sure you cover your fancy floor, if you got one.

It worked fantastically.

I hear that you can prevent this in the future by turning off the A/C a couple minutes before you park the car. I'll never remember that. I'll just spend the $9.00.