Air Conditioner keeps going out during the hottest part of the day?

We had a repairman come by and just stated that the filters had to be replaced more often (we had just changed them lest than 2 weeks ago) and stated that it could have gotten the Coils dirty and that they may need to be cleaned. Could there be another reason for it going out only for a couple of hours, then it tends to start cooling again? When it doesn't blow cold air, you can tell, by the motor not turning on?