An unusual uptick in empties in the normally busy summer season is seen as a sign that renters’ appetites are being squashed by rents setting new records since March. An unusually hot summer seems to be cooling off Manhattan’s market for rental apartments. In July, the vacancy rate rose 0.19 percentage points from the previous month, to 1.2%, in an unusual uptick for the normally busy summer season, according to the latest monthly rental report released Thursday by brokerage Citi Habitats. July marked the second consecutive month to see a rise in vacancies, a two-month run that brought them close to the levels of March, the report noted. In contrast, in July of last year, the vacancy rate stood at 0.86%. Rising rents may have something to do with that. Average Manhattan rents set yet another record in July, hitting $3,459 a month, up 3% from the same time last year. The average monthly rent for a studio hit $2,078 in July, while average one- and two-bedroom apartments’ rented for $2,812 and $4,001, respectively.