The leaves build up in 2 places: the cleanouts inside the fenders and against the evaporator core.
You can access the evap by pulling the motor & the resistor plate (big electrical connector and 2 small screws beside the motor) and you can reach in and dig leaves out or split the evap housing on the other side (facing the engine) and hose everything out.
The cleanouts are much more difficult. They are thin rubber valves (for lack of a better description) attached to the front lower corners of the firewall facing down & slightly forward. They're supposed to be thin enough to let leaves & acorns & solid objects to drop thru using road vibration to help, but they always clog up. You can try to reach them by climbing over the fender with your feet in the air and reaching down inside the back edge of the fender, but you'll only P!$$ yourself off and cut your arms. The best way to get to them is pull the little screws that hold the outer edge of the wheelwell onto the fender and pry it down. They can be PITAs esp. when their J-nuts break, but it's still less hassle. Just remember HOW THE WHEELWELL FITS TO THE FENDER - it goes inside in some places and outside elsewhere. Once you get to the cleanouts, squeeze them along the long axis to open the big slot and DIG IN!!![img]/wwwthreads_images/icons/smile.gif[/img] They'll be jammed with some nasty wet grimy $#!T, but you gotta dig it out by hand, then you can rinse water into the wiper valance and it'll drain out and finish the job. Be careful pulling on the cleanouts, though, since they're held on by 2 plastic rivets that are hard to remove if you pull the rubber off them. Here's what they look like:
For anyone who doesn't have an EEC, or who is desperate not to pull the wheelwell, you can pull the kicks in the footwells and remove the plates for the old "I'm too cheap to get A/C" vents and you'll be looking at the insides of the cleanouts. If you DO have an EEC, you can still get to the passenger one, and even to the driver's ('84-91 only) if you pull the EEC forward into the engine compartment.