A customer reports their air-conditioning system is running constantly but not cooling sufficiently, with a cold suction line and sweating compressor. What is the most probable cause?

The scenario describes an air-conditioning system that is continuously running, has a cold suction line, and features a sweating compressor. These symptoms are indicative of a problem with airflow, making restricted return air or a dirty evaporator the most likely cause.

When the return air is restricted or the evaporator coil is dirty, it can hinder the effective circulation of air, which means the system struggles to absorb enough heat from the indoor air. As a result, the compressor will attempt to compensate by running longer to achieve the set temperature, leading to constant operation. The cold suction line indicates that the refrigerant is not absorbing the heat it should, which further aligns with the symptoms of insufficient cooling.

A dirty evaporator can create an insulating layer over the coil, reducing its ability to absorb heat, while restricted airflow can prevent warm air from passing over the evaporator properly. Both conditions can lead to inadequate cooling despite the system's ongoing operation, which matches the customer's experience of constant running but insufficient cooling.

In contrast, a refrigerant leak would typically lead to a loss of pressure, hence warmer lines, and low refrigerant levels would also cause reduced cooling. Faulty compressor wiring generally would prevent the compressor from running effectively, not leading to the indicated symptoms. Therefore,