If you are getting a band of ice about 1 inch tall on the bottom of the fins of the air conditioner it's not serious. Probably the air conditioner is tilted a LITTLE into the room (it should be tilted back a bit and has to be HORIZONTALLY level). In some brands of air conditioner, there is only ONE channel, on ONE side of the air conditioner that passes the condensate that drips from the fins to the back of the air conditioner where it evaporates (or drips out).
If the air conditioner is tilted forward OR horizontally AWAY from that channel, water stays in the little catch basin in the front of the fins. As it builds up, it starts to freeze, and then it climbs and climbs if it goes unchecked it can freeze the fins to the point that the air won't be able to flow thru them.
That channel can easily get blocked with a small seed... or a bug... or lint that fell into the gutter and then made a "dam". Flush it out with water or an air compressor or use a coat hanger or wire to clean it out.
If the water gets trapped by the ice so it spills into the front fan-blowing area it will start to “spit” out the top. Melt the ice, flush the channel, make sure you are tilted correctly, and that's it!
SOMETIMES the problem is in the BACK of the air conditioner. The evaporator pan fills up with water. Just a little bit of dirt or algae can raise the water level too much. Again, depending on angle, it might get so high that the fan can start picking it up and “shooting” it back into the room! Gross! Clean out the drip hole and/or the pan in the back of the AC.