A/C needed in Zurich in August?

Of course, there's no way to predict with accuracy what the weather is going to be like when you are there. It might be mild and comfortable. Or there might be a heat wave. If it were me, I'd plan for the possibility that it'll be hot. A year ago it was uncomfortable enough to make someone grouse about it in their hotel review. Unless that review was full of irrational ranting (enough to make me question its credibility), I'd heed that warning.

Can you live with being possibly hot and uncomfortable while you try to sleep? If yes then no problem - you don’t need AC.

Otherwise bite the bullet and reserve the room with AC.

Oh my! I can not reply fast enough! Do NOT stay at Bristol! I dont care if Rick recommends it. We were there in MAY in 2018. No A.C., just some little fan in the room. It was unseasonably warm. We were on the 3rd or 4th floor, and we were too warm. So, we opened the window and were left sleepless due to the road noise, the pedestrian conversations and the party on the balcony below us. The room was sterile feeling; the towels were very thin, and the breakfast was the worst of our whole trip. ( Unless you consider fruit cocktail from a can as breakfast worthy.) The whole hotel is stuffy with no air moving. Choose the other hotel, PLEASE!!

You should be generally okay. The problem is that, when a heat wave strikes, you get several days with warm nights and progressively warm building walls. It can get rather uncomfortable at upper floors and borderline unbearable on top floor.