Suction lines must be ________ to assure proper oil return.

Suction lines must be trapped to ensure proper oil return in a refrigeration or air conditioning system. Trapping refers to the creation of a low point in the suction line where oil can collect, helping to prevent oil from pooling or getting trapped in other parts of the system. In systems where oil needs to circulate with the refrigerant, proper oil return is critical to maintaining lubrication for the compressor and ensuring efficient operation.

When oil return is not adequately managed, as can happen when suction lines lack traps, it can lead to compressor failure due to insufficient lubrication, which ultimately affects system performance and lifespan.

While options like raising the lines, using slightly oversized lines, or insulating might help in specific scenarios, they're not the primary method for ensuring proper oil return in a suction line. Traps serve a vital role in overcoming gravity and allowing oil to flow back to the compressor efficiently.