Final answer:
The true statement about adding oil to a system is that oil is added by charging it into the crankcase. It is important to follow manufacturer's guidelines when performing this maintenance task to prevent any issues such as contamination or incorrect oil levels.
Step-by-step explanation:
The question relates to the process of adding oil to a system, specifically a system involving an internal combustion engine. The student is asked to identify which statement regarding this process is true. When addressing this, it is important to consider the operation of such engines and the practical aspects of engine maintenance.
Among the given statements, the correct one is: Oil is added by charging it into the crankcase (A). The crankcase is a space at the bottom of the engine where oil is stored and from where it is circulated. Oil is indeed added to the system, typically when the engine is off, through a designated fill port, which may sometimes be directly through the crankcase or through another component that leads to the crankcase. It's critical to follow the manufacturer's procedure when adding oil to ensure no contamination occurs and to maintain the proper oil level.
As for the other statements, they generally contain inaccuracies. The crankcase is subject to variations in pressure during the operation of the engine, so it is not accurate to say that air cannot get in when adding oil (B). Oil can often be added when the compressor or engine is not in operation, making the statement (C) incorrect. It is not typically necessary to recharge, purge, and re-pressurize the system after adding oil, which nullifies statement (D). Regarding statement (E), while adding oil through the dipstick tube may be possible in some compressors or engines, it is not the standard method for most compressors and hence cannot be taken as a universally true statement.