Residential HVAC Installation Practice Exam 2024 - Free HVAC Practice Questions and Study Guide

The correct answer is B. Refrigerant and oil are the only two substances that should be in the refrigeration system for proper operation. Refrigerant is responsible for absorbing and releasing heat, while oil is necessary to lubricate the moving parts of the compressor. Together, they ensure the efficient and smooth operation of the HVAC system. Option A, refrigerant and lubricant, is incorrect because lubricant is not the correct term for the substance needed in the refrigeration system; it should be oil instead. Option C, compressor and oil, is incorrect because the compressor is a component of the system, not a substance that should be present in the refrigeration system. Option D, lubricant and coolant, is incorrect because coolant is not a substance used in the refrigeration system; refrigerant is the correct term for the substance in this context.