Which of the following components is common to both heat pumps and air conditioners?

The component that is common to both heat pumps and air conditioners is the condensate trays and lines. Both systems operate based on the principles of heat exchange, where excess moisture is often a byproduct of the cooling process. During operation, moisture from the air condenses on the evaporator coil, and the resulting water needs to be drained away. Thus, both heat pumps and air conditioners are equipped with condensate trays and lines to manage this drainage.

In contrast, while the other options, such as expansion valves, heat exchangers, and compressor motors, may also be components found in both systems, they do not serve the same ubiquitous function as condensate management. Expansion valves and heat exchangers have more specialized roles in the cycling of the refrigerant, and while compressor motors are essential for the function of both systems, their presence is not as universally noticeable in the context of moisture management.