Ice forming on the small liquid line is an indication of low gas pressure. Either you have a gas leak or its due to a restricted valve/capillary tube.

BUT!!! if it ice is on the suction line (picture below), do not top up gas. It means that the aircon in the room is not fully evaporating the liquefied gas. This can be caused by several reasons:

1) The fan motor in the aircon blower is not turning (either jammed or faulty). Under such a condition, the indoor fancoil will ice up too. Or had you set the remote controller to “dry”. That will occasionally stop the fan motor, and when the fan is spinning, the motor will be spinning slowly. If it is caused by the “dry” mode, the fan coil will not ice up, but the suction pipe may ice up.

2) The compressor is still running even when the aircon is turned off (therefore fan is not turning). This will be caused by a jammed magnetic switch.

3) Having mentioned above that icing at return suction line is caused by the blower not fully evaporating the liquefied gas, an oversized compressor or an undersized blower will cause icing on return line too.

4) In respect to point 3 above, if your indoor aircon blower is badly choked up, technically speaking, your blower becomes “undersized”, isn’t it. If it is so, you will find that the air is not coming out strong. You’ll need to conduct a thorough Chemjet to unchoked it.

Following is a picture of an iced suction pipe, which is the bigger pipe. Usually, the suction pipe is the one with the 
charging valve.