I faced the same AC cooling problme in my car with ice on AC pypes.
Reason was that my car didi not have AC thermostat and compressor kept
on working keeping the air more n more cool and ultimatelyy water on the pypes starts converting the into ice which ultimately eaffects the wokring of the AC system.
There are 6 or 7 options on the AC switch.
When the cooling is reduced and ice is there on the pypes then this AC switch should be moved to the option of fresh air, means no compressor working. Air will be cool again. I used this alternate option for a month subsequently installed a thermostat in the car and now no ice is there on the pypes.
Your car may havesame problem, check the above procdedure in your car, i hope it will work. If it works then go for a thermostat installation.