I live in an apartment with a heating and cooling system that uses water pipes. I'm not familiar with this. My air conditioner blows warm air and when the man from the A/C company comes to check it. He says it's working fine but then a few days later it happens again. What is going on?

Someone help,, I`ve no experience with a/c that uses water pipes

There are many things that could be wrong, A relay, A valve, A contactor.
About the only way to make sure is to do a test in the field. A good A.C. Man could find the problem in a short time, now doing the repairs is a different matter it could take him hours.