Which of the following aspects is critical to check during an HVAC system installation?

During HVAC system installation, ensuring connection tightness is critical for several reasons. Properly tightened connections help prevent refrigerant leaks within the system, which could lead to reduced efficiency and potential system failure. Leaks not only harm the performance of the HVAC unit but can also have environmental impacts, especially regarding refrigerants that may contribute to ozone depletion or global warming.

Tight connections also ensure that air flows smoothly through the system without loss, thereby optimizing the efficiency and longevity of the HVAC equipment. If connections are loose, it may result in air leaks, which can lead to increased energy consumption and higher utility bills due to a system needing to work harder to maintain the desired temperature. This attention to detail is vital to the successful operation of an HVAC installation.

The other options, while important to the overall functionality of the HVAC system, do not carry the same immediate criticality during installation compared to ensuring that connections are tight and secure.