bad smell when AC is on (94 E420)

i searched the posts for similar topic and i was able to find some related info but i wasn't sure if i got the answer. so here goes.

i recently bought a 94 E420. the car is great except for a bad AC smell. it is only observed for 10+ seconds right after the AC is turned on. (there appears to be no smell when the heat is on, though). after about 10+ sec, the smell goes away.

i brought the car to a local dealer and they weren't much help. they used a product called ozium that's supposed to get the smell out but it didn't help.

can someone help please? i want this car to be perfect.

the car has very low miles (< 40k) so i am guessing that the AC wasn't used much. could that be the reason?

anyinfo would be very helpful.

thanks