Not so safe, but it all depends where you live in the city and all that. Downtown / midtown is the best, anything else is hit or miss. Areas on Moross St. by Grosse point are just as nice as anywhere else. Also, even though Detroit is arguably the most dangerous city in the country, suburbs are very safe.
Air conditioning tonnage has nothing to do with weight. A ton, as used in the HVAC field, is a term that describes how much heat the AC unit can remove from a home in one hour. The measurement for heat is the British thermal unit (BTU). One ton of air conditioning can remove 12,000 BTUs of air per hour. A four ton unit can move 48, 000 BTUs and so on. Therefore, the more tonnage an AC unit is rated at, the more air it can cool.
A ton of air conditioning is not related to weight. A ton of cooling is equivalent to 12,000 BTU or 3.5 KW. This is the measurement unit for moving thermal energy. A 1.5 ton AC will move 3/4 of the amount of heat energy as a 2 ton unit, the 2 ton unit will be able to cool a given space faster.