A mass-excavation contractor reported that a Komatsu PC490LC-11 crawler excavator had developed a progressive air-conditioning fault over a four-week period. During the first hour of a shift, the cab's air conditioning blew cold air normally. As the shift progressed and cab temperatures rose in summer conditions, the A/C output would progressively warm - eventually delivering only ambient-temperature air and allowing the cab's interior temperature to climb above 40°C during peak afternoon conditions. The operator also reported that the cab windows would intermittently fog during hot weather, requiring manual defrost activation, and that the fault seemed to worsen when the machine was working under heavy hydraulic load - exactly the conditions that produce maximum engine heat and cab heat load. The operator's productivity was measurably affected, with rest breaks required to escape the overheated cab.
The technician first verified the symptom by operating the excavator with a loaded bucket under heavy hydraulic demand while monitoring the cab's A/C output. Within 30 minutes of heavy-duty operation, the A/C output had warmed noticeably, and the compressor's sound indicated intermittent disengagement - the characteristic "clicking" of the electromagnetic clutch cycling on and off rather than running continuously.
He connected the refrigerant manifold gauge set to the A/C system and monitored pressures across a loaded test cycle. During normal operation, the low-side pressure read approximately 2 bar and the high-side pressure read approximately 18 bar - within specification. During the fault events, the low-side pressure would rise to 3.5 bar and the high-side pressure would climb to 26 bar - far above the normal operating range, indicating the condenser was not rejecting sufficient heat from the refrigerant. This pattern suggested either a condenser cooling restriction or insufficient airflow across the condenser's fins.
He inspected the condenser - the heat exchanger mounted ahead of the engine's radiator that rejects heat from the refrigerant. The condenser's fins were visibly packed with quarry dust, sand, and fine aggregate particles, forming an insulating layer that restricted airflow through the condenser. He also inspected the cab air filter, which was heavily contaminated with fine dust, restricting the cab's airflow and reducing the evaporator's ability to absorb heat from the cab's air - compounding the A/C output reduction. He further inspected the A/C compressor's electromagnetic clutch, and found the clutch's friction surface showing visible glazing and uneven wear - a condition that reduced the clutch's grip when hot and caused the compressor to intermittently slip and disengage during high-demand operation.
The root cause was traced to condenser cooling restriction compounded by cab filter contamination and A/C compressor clutch wear. The contaminated condenser fins had restricted airflow and raised refrigerant high-side pressure, forcing the compressor to work harder and causing the clutch's friction surface to overheat and slip. The contaminated cab filter had restricted the evaporator's airflow, compounding the A/C output reduction and reducing cab cooling capacity further.
The repair involved pressure-washing the condenser's fins with low-pressure water (taking care not to damage the delicate aluminum fin surfaces), replacing the cab air filter with a new element, and replacing the A/C compressor's electromagnetic clutch assembly with a new unit. The A/C system's refrigerant was recovered, the system was evacuated and leak-tested (no leaks found), and the refrigerant was recharged to Komatsu's specified weight with fresh compressor oil added. The condenser's cooling fan and fan clutch were inspected (both within service limits). After reassembly and a loaded 60-minute test cycle under heavy hydraulic demand, the A/C output remained cold throughout, the cab's interior temperature remained stable at 22°C, the windows did not fog, and no compressor clutch slipping was detected. Condenser fin cleaning and cab air filter replacement were added to the machine's 250-hour preventive maintenance checklist, with additional cleaning recommended during dusty-season operations.
