usually peepur call for service (clean) once every 3 months or you can stretch a bit if you dont use often.
the easiest thing you can do is just DIY clean the air filter (open the flap and take out the filter and wash with some soap/water, wait dry then put back) = do so once a month?
u can see how the technician clean. if you think u can DIY what they do, then you actually could!
i have been DIY-ing for a few years now, there are many online youtube videos and an EDMW thread here also on DIY aircon cleaning
btw gas top up scam i kena before. no need to top up one. if u need to top up means got leakage, top up also useless, gotta top up again and again each time 100+ no use coz root of leakage not solved