I am from South Texas, it is very hot here in the summertime so air conditioning is a must. I live in a 50 year old house and of course back then there was no central A/C so my home is cooled with window units but it works out alright. One of my units the larger one of the three that I have in the house is a 12000 BTU unit is 13 years old it is a Carrier. I have taken very good care of it through out the years but recently it has started but make a deep humming noise and it is not cooling as well as it should. Should I find someone to look at it or maybe someone can tell me if I might be able to fix it. Another question would it be cost effective to fix it or just buy another one.