What should the technician check if a refrigeration system is not cooling effectively?

The correct choice focuses on the essential components that directly impact the cooling efficiency of a refrigeration system. When a refrigeration system is not cooling effectively, it is crucial to assess both the compressor operation and the refrigerant levels.

The compressor is the heart of the refrigeration system; it compresses the refrigerant and circulates it through the system. If the compressor is not functioning properly, it can lead to inadequate pressure levels and, consequently, insufficient cooling. Additionally, checking the refrigerant levels is essential because low refrigerant can indicate a leak or undercharging, which directly affects the system's ability to absorb heat and cool effectively.

By checking these two aspects, a technician can identify common issues that lead to cooling problems, making this the most comprehensive approach for troubleshooting system performance.