Sorry, our air conditioning is not working right now, that's why it's so hot and sticky in here.
We have another store close by if you'd like to go there.
この場合、次のように言えますよ。
ーSorry, our air conditioning is not working right now, that's why it's so hot and sticky in here.
「すみません、今エアコンが故障していて、店内が蒸し暑くなっています」
hot and sticky で「蒸し暑い」と言えます。
ーWe have another store close by if you'd like to go there.
「よろしければ近くに別のお店があります」
姉妹店は sister store と言いたいところですが、これは不自然な言い方ですので、このように言うのが良いかと思います。
ご参考まで！
The AC has broken so it will become hot and humid.
"エアコンが故障してしまい店内は蒸し暑くなっています"
- The AC has broken so it will become hot and humid.
- The air conditioner has broken down so the inside of the store will become hot and humid.
「近くに姉妹店があるのですがいかがですか？」
- There's a sister store nearby, would you like to go there?
- Would you like to go to another store that is nearby?
カナダ 
アメリカ合衆国 
