It is normal for ice drops to form which then melt when your machine defrosts. A light dusting of ice on the rear wall indicates your machine is working ok.

Ice will accumulate at the rear of the appliance

Check the setting of your thermostat control, if set on a high number or the 'max' position on the dial then the fridge will be too cold resulting in an ice build up. Try reducing the setting, the mid way point on number 3 on the dial we find works fine! You don't need to turn it up in the summer.

The larger the number you set, the colder the fridge will become, thus setting 5 is far colder than if set on 1.