TLDR: The AC in the rooms do not work well. Our experience was that it would work for 40 minutes, then system would error and shut off. We were in London when the temps were 84F/29C, so quite warm and necessitating AC. I would NOT advise anyone to stay here when its warm outside.
Long version - I am from the US and accustomed to AC, so I made sure to book a room with AC when visiting London. Upon check in to the room, it was warm, but we turned on the AC, and it seemed to be blowing cool air, so we left to explore London.
When we came back in the evening, it was well over 80F in our room, and the AC didn't seem to be working well. Asking the evening staff member for help was useless. She was disinterested and unhelpful. After googling the thermostat in the room, I figured out how to specifically turn on the AC (it was on fan mode). However, after approximately 40 minutes, the AC system errored and defaulted back to fan mode (no more cool air).
I spoke with staff about this, was told maintenance would look in the AM. The next morning, was told maintenance isn't available (because weekend), so they moved us to another room. That evening, after the daily temps were 91F/33.7C, we came back to another hot room, that didn't cool off. The evening desk person wasn't even available to speak with. The AC acted the same as the previous room, so after approximately 2 hours we decided to leave and stay elsewhere for the duration of our trip.