Has your apartments AC system stopped working?
If you live in an apartment complex and your air conditioning has stopped working you need to contact one of the residential HVAC contractors in your area. Many times the company that owns and operates the complex will have a contract already with one of the local heating and cooling companies.
The first thing you should probably do is contact the front office to see if they do indeed have a certified heating and air company that they have already signed with. If they do indeed have a contract with someone you will have to use that company if you do not want to pay for the services out of your own pocket.
Now, this information really only applies to apartment complexes though. If you live in a condo complex the odds are that you will be responsible for all air conditioning and heat pump repairs yourself. This is one of the downsides of renting or owning a condo. If you are renting a condo you should probably check with the owner to see if they have signed any paperwork with a local company before calling someone yourself.