Which system components are commonly responsible for refrigerant leaks?

The correct choice highlights components that are often involved in refrigerant circuits and are particularly vulnerable to leaks. Compressors, evaporators, condensers, and fittings are integral parts of a refrigeration system.

Compressors are involved in pressurizing the refrigerant, which can lead to potential leaks at the seals or gaskets due to wear or overheating. Evaporators and condensers involve the phase changes of the refrigerant, which can create stress and lead to leaks, especially where connections are made to fittings. Fittings themselves are common leak points since they are joints that connect various sections of pipes or components. Over time or due to thermal expansion and contraction, these connections can develop leaks.

The other options, while comprising important elements of HVAC systems, do not typically account for the main areas where refrigerant leaks arise. Thermostats and relays do not directly handle refrigerant, and while piping and insulation may serve to protect and contain refrigerant, they are less prone to leaks than the actively functioning components mentioned in the correct answer. Coils and expansion valves do play roles in refrigerant flow but are not as frequently associated with leaks as the primary system components listed in the correct choice.