[ClockworkC5]

ice forming on the air handler coil could be caused be a number of things. air blowing across the coil at a reduced rate, enough so that an optimal heat exchange rate is not met (not correct volume of air blowing across coil leads to the coil operating at a temperature much lower then design intent) causing the coils to super cool and freeze the condensation that constantly forms on the coils. this could be caused by a clogged filter, dirty coils, failing blower motor, damage to the fan, or low freon. the air handler at your house operates similiar to the one in your vehicle. if youve ever been low on freon in your car you will hear your compressor cycle on and off. this is because the compressor will not engage unless it has sufficient freon. when the correct amount of freon is on the suction side of the compresor, the compressor will engage and continue as long as a sufficient freon is fed to it. as soon as the compressor engages, in a vehicle low in freon, the freon pressure will drop resulting in the compressor kicking off again. your residential unit does the same thing. so it will super cool the coils in spurts, causing icing of the coil. check to ensure that your compressor (outdoor unit) is engaging and consitant to start ruling out some things. but most likely you have a freon leak. tracing the leake can be difficult and time consuming, however many times the leak is as simple as the test ports for the freon lines leaking. if the unit has been serviced for this in the past the service tech would add a green dye to trace the leak. if not, just look for a dirty part in the lines. a leak will leak freon into the atmosphere, but leave behind the compressor oil. this remains on the pipe and attracts dirt and grime. if you find something like this, clean it, and check after a day. hope this helps. let me know if you have any further problems or questions.