When I turn the air conditioner on after being off for a day or so I notice a rotten egg smell for the first few minutes the air is on. What is causing this smell?

Not sure about the air conditioner, but I know in the winter when we turn on the heater the first day it smells like that. I was told when I was younger it's because all the dust is heating up and letting off that smell. Hope you find your answer.

your evaporater coin needs a good cleaning,they make several products and can be biught at most furnace a/c distributers or parts houses,,,,,,

sorry,,,,,,evaporater Coil,,,not coin

wmproop is correct. You have dirty socks syndrome. It is a common problem.