Powder, I believe the Teco Micro is a thermoelectric chiller and does not use refrigerent. Not sure if the A/C man can help. You might want to check with the distributor here in SG. You may also contact the manufacturer directly for feedback/ideas on what to do or how to troubleshoot.
Have you added any new pumps/powerheads/lights lately that would cause the temp increase?
Personally, for my 2ft (2x1.5x1.5), I'm using the Teco TW4 (RA240). For cooling, IMO, the more powerful the better... although the TW2 would have probably sufficed for my tank. I got mine 2nd hand from a fellow reefer... so far so good.