If all is perfect you may get a 20° drop but it may take all weekend. I had mine checked and the charge adjusted by a tech 2 years ago and it has been working well. (knock on wood) Ours was estimated at 40+ years old. If it is sized correctly if it runs constantly when the ambient get's close to 100°. Removing the humidity is the important part. Our's is most comfortable at 77° with around 45% humidity. Make sure the compressor coils are clean. A clean filter inside as well. I was able to get into the evaporator and clean about a lott that got past the filter. (our filter system sucks)