I have a 15 yr. old residential Trane unit . Last year it was cooling OK. We did not use it as much over the winter time (Florida) .Summer picks up now and we notice that the AC is running forever and not cooling as much as it did last year. Coils are clean and so is the filter also I cleaned the outside unit coils. Is this unit giving up or does it need freon refill ? Any suggestions ? Thanks.

Could be low on refrigerant or it may have other problems. 15 years in Florida is great for any AC unit. Your compressor could be going bad and not pumping at the same capacity it use to. I know you said the coils were clean but next time you have the AC turned on, feel the smaller of the two lines coming off the outside unit. If it's hot, your outside coil is dirty or your fan is'nt moving enough air through it. Sometimes condenser coils can look clean on the outside but they can be plugged up internally and will require a good cleaning.