Chlorine treatment is considered one of the most important processes to obtain high-efficiency CdTe solar cells. Such treatments are usually performed by exposing the devices to CdCl₂ or other chlorine compounds and annealing them at high temperatures. Annealing processes were carried out in vacuum, inert atmosphere, reactive atmosphere, or air. The usage of ambient air has several advantages either technical or economical. However, the presence of moisture in the atmosphere may affect the treatment results or their reproducibility, especially in countries where the relative humidity (RH%) of the air could be an issue. However, despite many reports on CdTe Cl-treatments, the RH% effect on the finished solar-cell performance was not extensively reported. In this work, RH% was varied from 0% to 60%, comparing two different Cl treatments: CHClF₂ (gas) and CdCl₂ (in MeOH solution). It was observed that the RH% negatively affects the electrical properties of CHClF₂-treated solar cells, while it could reduce the spatial uniformity using CdCl₂. We conclude that relative air humidity is a parameter that should be controlled for producing high-quality CdTe-based PV devices.