What can cause an AC unit to not cool properly?

An AC unit not cooling properly can be attributed to several factors, each of which can impact the overall performance of the system. High refrigerant levels can create issues with the pressure within the system, leading to inefficiency in the cooling process. If the refrigerant levels are too high, it can hinder the function of the compressor and other components, ultimately affecting the cooling output.

A failed thermostat can also be a significant issue. The thermostat is responsible for detecting the indoor temperature and signaling the AC unit to turn on or off accordingly. If it is malfunctioning, the air conditioning system may not operate as needed, resulting in inadequate cooling.

Additionally, a clogged drain line can obstruct proper drainage of condensation. This can lead to water buildup, which may affect the overall performance and cause the system to freeze up, further impeding its ability to cool effectively.

Given that all of these factors can independently lead to a decrease in cooling efficiency, it's clear that each one can contribute to the problem of an AC unit not cooling properly. Thus, the option that encompasses all of these potential causes accurately reflects the range of issues that should be considered in troubleshooting the AC unit.