AC needed Lucern in late June?

You might want to check timeanddate.com which has weather information at different times each day from the past @ 20 years.

It looks as though Lucerne has seen some hot weather in past Junes.
Have you tried Booking.com? You can plug in filters (AC) in your case for hotels and for apartments. I've used them often and then go directly to the hotels'/apartments' websites to see if I can get a better deal. Sometimes Booking.com has had the better deal which, for me, also includes being able to cancel late without a fee.

AC is always a must for me, too. We were in Paris early September when the temps reached 95 and 96 consistently for @ 10 days. You just never know!

June 2022 in Lucerne, my hotel (Des Alpes) did not have a/c, but they provided a fan. The room was stuffy. I have the same hotel booked for next June, so it must not have bothered me too much.

Hotel des Balances does have a/c and I considered it. But, I just couldn’t justify the additional expense.

Maybe we’ll both get luck and next June won’t be as warm. 😊

Window screens are not a thing in most of Europe, but I do not remember Lucerne being that "buggy". And it is not a large city so it does cool down at night. This being said... without A/C, an Airbnb will be easier to manage than a hotel room, because hotel rooms typically have just one window, so there is no possibility of a cross-breeze, and the cooler night air won't come in. I was quite uncomfortable at a top-floor hotel room in Hotel Stern in July in the mid 2010s (2017 I think?).

Carrie, we have stayed at Hotel Des Alpes on the lake side, overlooking the Chapel Bridge, ( both times fall.) I remember getting a good breeze, and bugs not being an issue. The rooms are above some restaurants , but they seemed to calm down/ close around 11pm. If you can get a balcony room, it's so nice to just sit and people watch, and sometimes see Mt Rigi in the distance. The morning views are spectacular . And the farmers markets are lovely on Saturday mornings, fresh bread, yogurt, cheese for breakfast in the crisp morning air.
I'm jealous!

We were in Lucerne 6 the first week of September and were very grateful to have A/C in our hotel room. Sleeping at night without it would have been miserable. I too was reticent to spend that much money for a hotel room. After extensive research comparing facilities, price and location I chose Hotel Beau Sejour and that turned out to be a great decision. They describe the A/C as a portable unit, and that had me questioning its efficiency, but it cooled the room very well. We had a historic double room with no lake view. The hotel's staff is extremely professional & we enjoyed a terrific breakfast each morning on their lake view terrace. The walk from the hotel along the lake to the city center is peaceful and beautiful. It was very quiet at night since we were not in the midst of the tourist zone's hustle and bustle. I would stay there again when visiting Lucerne.

Whether or not you need A/C is a personal preference. (I like A/C).

I've stayed at the Ameron Hotel Flora twice and it has air conditioned rooms. (Not sure of the price). Nice included breakfast buffet.

It's located one block from the lake and the Chapel Bridge and less than a 10 minute walk to the train station.

Pat, I did splurge for a bridge view this time. But you know what, I don’t have a balcony. Ok, I just changed my reservation for one with a balcony. What’s another $100 when it comes to Switzerland. 😊

We too were in Luzern in early September and chose the Continental Park (recommended by RS) because that hotel is air-conditioned and just a short walk from the train station. The concierge, Ms. Haas, went above and beyond for us 5 couples. She obtained tickets for a free Luzern Festival concert at the KKL hall, arranged for Pilatus tickets, etc. 3 rooms were ready for us when we arrived before noon. The CP has an unserviced rooftop terrace (no great views) which was perfect for enjoying a glass of BYO wine in the evenings. We opted for the breakfast which was good but spendy.

It was HOT in Switzerland! After Luzern we stayed in Wengen in a penthouse w/o AC and it was warm for sleeping, especially with those duvets! Hiking from Mannlichen to Kleine Scheidegg it was shorts and tank top weather. My puffer vest never left my suitcase.

Carrie, once again I am jealous because balcony rooms were never available when we have been at the Hotel Des Alpes. I will always have a warm spot in my heart for them when they didn't charge us in 2021 when our flight was canceled and we spent an unplanned night in Chicago. They were well within their rights to charge us. We will return! Safe travels!