The obvious one is to check the filters. If they have not been cleaned for several months they could be completely blocked and not allowing any airflow allowing you to believe the air conditioner system is not working properly. This could be a cheap simple fix so check this first. Secondly confirm your remote settings are correct and not on the auto settings. If you have lights flashing on the indoor unit and the air conditioner is not working it is giving you a fault code. Depending on the error code you may be able to retrieve the error from the remote or the number and type of flashing lights depending on brands. If you are able to get the error code it could save a second visit as the technician may be able to bring the required parts associated with your error on the initial call out so make sure you advise the company of what the error is as well as your model number.