When it is a real hot day out and you have no air conditioning it can be a very bad and potentially deadly thing depending on where you live in the country.
Some places can get by with no air conditioning on a hot day with just a fan if you live in a gradual climate where it does not get above 90 degrees as a hot day, and then it cools down at night. But if you live in a place like Arizona, you will need to have some form of very powerful air conditioning twenty four hours a day and seven days per week or you will surely die. Because temperatures there can get up to one hundred and twenty degrees! It is seriously deadly. And without air conditioning there is no survival. I have lived in that area of the United states of america before. And it is no fun let me tell you! Even if you have the most top of the line, brand new, up to date and extremely expensive central heating and air conditioning system, the heat can get to be so damn bad that even the air conditioning out of one of those top quality systems will even not be good enough. You will have to sometimes have a portable air conditioning system to help cool your home in addition to the air conditioning from your central heating and cooling system unit! But thankfully I do not live there anymore and in the event I have a serious air conditioning system breakdown, I could get by with a fan for one single day and night. But I feel for those who can not.