A/C

As a for instance there are 5 Premier Inns (a mainly English budget chain) in Dublin- 4 of those have air conditioning.

This comes up a lot but I’d be so surprised if you needed it. I have spent a lot of time in Ireland and never once have I used air conditioning nor felt I needed it. I have, however, felt very cold and wet and wanted good heating or a fire. The reason most places don’t have it is because it is not necessary.

Depending on when you are travelling, don't get too hung up on this. We northern Europeans largely manage without.

Go to Booking.com and do a search. You can filter for hotels that offer a/c.

I will uses Booking.com to search for the hotel I prefer but then I book directly with the hotel.

It's Ireland - there's a reason why there isn't air conditioning.

The fact that some of the reviews you've read were complaining about it rather implies that some people needed it but didn't have it. Though you're unlikely to need A/C for most of the year, summer days in Dublin can get pretty warm making things a bit stuffy and uncomfortable in the room - resulting in a poor night's sleep.
We certainly would have liked to have had it on our most recent trip to Dublin (in June).Comes down to your relative tolerance I suppose. My wife has none and needs it cool for sleeping, hence my marching orders to ensure we have it when booking a place ... unless it's absolutely arctic outside. YMMV.

Aren't you going in late October? You definitely will not need AC in October.

Thanks for all the input!