the leaking sound is the expansion valve functioning, it flows any remaining gas in the liquid line.
If you are topping up gas every 30 days, you have a big leak and need to have it fixed also fix the blower speed selector, most probably the resistor block is bad. Find yourself a good A/C tech to repair this leak. If your low side line is not sweating then the system is severly undercharged or have a bad expansion valve or you live right in the middle of Thar desert.
I think you have a bad A/C mechanic and is just giving you a run around because you did not buy the condenser from him.