Sure enough the different buses had different levels of cooling equipment and air conditioning quality.
I recently took a actually long trip across the country. I went from actually far north to the south. It took a few mornings on the bus, and the bus would stop often, at different stations and cities and periodically even for a few minutes, and the two of us could go and get some food or even see a bit of the town or town that the bus stopped at. Sometimes the bus would be changed too, or the driver would change. The main concern was that the air-conditioning or the heating in the buses would really vary, up north where I started it was pretty cold when I left, so the bus needed wonderful heating, however but the air ducts just did not supply the sizzling air the bus needed. I felt like I might even catch a cold. Then the buses were changed at a single of the stops, and this time the up-to-date bus had really strong heating. It felt like a gas furnace in the bus. It was really uncomfortable. As the two of us went further south it got warmer and warmer, until it was pretty hot. Sure enough the different buses had different levels of cooling equipment and air conditioning quality. I was blessed I had a heavy coat! It was kind of surprising the air quality and the temperature levels in the different buses were so different that is for sure. At the end of the morning the price of the ticket was OK though. It was not that cheap though. But it was a pretty efficient and safe trip, and that is the main thing.