Air conditioner problems!?

Yesterday our air wasn't working and when I checked the fan outside I noticed there was ice buildup around the hoses leading to the house. To try and thaw the system, I changed the temperature setting on the thermostat from "cool" to "off", and changed the fan setting from "auto" to "on". I let that run for about 3 hours and when I turned the a/c back on it seemed to be working properly again. I also put in a new filter. A few hours later it stopped again but there is no ice buildup this time. Very little air is coming out of the vents. Did I not thaw the system properly or could there be another problem?