My symptoms were similar...
1. takes a long time to cool - turned out to be a faulty relay switch, RM90
2. insufficiently cool during hot days - fixed after naidu serviced the system
3. a few days after that, totally no air from aircon - M1 identified a problem w resistor - RM430++
Now, I have to turn the aircon down! Freezes, esp during rainy days! Heaven!
Naidu is at Jalan Gasing, behind the Shell station, just next to the EPF building that you can see from the Federal Highway. Naidu is located right behind the Shell station.
In your case, the cooling coil may be suspect, in which case, a full dashboard down job is to be expected... good luck...