I have a 1 1/2 year old rheem 13pjl36a01 3 ton 13 seer, and it runs all the time. I set the thermostat to 75 during the day and when I get home, the temp is 78. I then set it to 73, and it usually doesn't reach that temp until 11:00 pm. Ay ideas what could be wrong? My home is 1680 sq ft, so I thought this was the right size unit.

If it worked well last year, the outdoor temps are similar, & there haven't been any changes in your lifestyle or shading on the house, something has obviously changed. I would suggest calling the installing contractor & have them take a look.

One clue is it does cool at night. Could be solar load overcoming BTU capacity. Trees shading house? Good windows and R30 insulation in attic? Lots of windows on South and West side of house. What is daily high temp? Some parts of country are experiencing a "late summer "-92 in Minneapolis! Right now, 11PM, it is 74 in Minneapolis and 72 in Atlanta

Thank you for the response. Yes, it cools at night. I live in Mobile, AL and it is 77 degrees right now. Highs are in low 90s, and there is little shade on the west side of the house, but there are large windows on that side. It has run non stop since I arrived at home 5:00 and has gone from 78 degrees to 74 degrees currently. Last night, I sprayed the outside unit to clear any possible debris/dirt from the coils, but it has not seemed to have made a difference. Another thing is the attic ventilation fan no longer works. The motor must have burned out late last summer... could that be the culprit?

The attic fan could certainly have an influence on the A/C. Do all you can to reduce the solar heating through those west windows. Blinds, shades, curtains, & awnings all help. If those west facing windows are on the back of the house, reflective film is pretty effective. Most people don't want it on front facing windows. If I had my way, my place would be dark as a cave in the summer.