If it turns out the air conditioner is clean but not cold, the second step that you can do is check freon gas pressure. Please install your manifold on nepel to fill freon on the outdoor unit. See if there is still pressure or runs out to ZERO. If there is still pressure, maybe only less freon. and this is practically reasonable. The cause can be from a smooth leak that may be difficult to find the leak, also from the slack nepel. The solution please tighten all nepel bolts, then add freon pressure with the same freon type on the AC. Which of course must be in accordance with the maximal ampere (strength) limit of the AC compressor machine. In the meantime, you might want to visit http://www.airconservicingsingapore.com/ as well.
Whereas if the needle on the manifold shows the ZERO, the freon pressure runs out. This is due to leaks, this can happen to an indoor evaporator, outdoor condenser, installation pipe, nepel pipe connection to indoor, or nepel that exist in outdoor. Steps you can do are:
Recharge the freon to full, usually 80 – 90 PSI, and 125 PSI for AC Inverter. Then open the indoor and outdoor body, do not forget to open also amarflex wrapping pipe AC. Take a sponge soaped with foam.
Then apply foam to all copper pipes and also condenser and outdoor. Look and watch carefully whether there is an air bubble or there is a good oil in the pipe, evaporator, or condenser. If there is an air bubble or oil it means that the leakage point of the freon.