I use one of these every year in both cars (X3 and Prius)

http://www.fasteronline.co.uk/comma-...er-p-2706.html

But obviously we are in the UK so you'd need to find the same product in the US.

Works like a charm - you start the car, run the AC on max and then set this thing off in the back of the car behind one of the front seats - it sort of creates a fog in the car which the AC then condenses onto the condenser coil, it cleans and sanitises the coil killing the bugs, and leaves a nice fresh smell in the car.

You can tell it's working as you will get a huge puddle of condensate under the car which is the run-off from the 'fog'.

One treatment per year and I no longer ever get that nasty stale smell