An aircon compressor has internal moving parts that are lubricated by the refrigerant oil circulating through the system. When those parts start to wear, they shed metal particles into the oil. That contaminated oil circulates through the entire system before the compressor fails completely.
The condenser is a heat exchanger with fine passages. Metallic debris and sludge from a failing compressor collects in those passages, restricting flow and trapping contamination even after a new compressor is fitted. A new compressor pumping against a blocked, contaminated condenser will overheat and fail prematurely. That is why we advise replacing both parts once the compressor oil is dirty, so the new compressor does not start against a contaminated condenser.
In Singapore's heat, a failing compressor deteriorates faster. The system runs harder and longer to maintain cabin temperature, which accelerates wear on a compressor that is already struggling.