Why is my AC running but not cooling?

Start with the things you can check yourself. Pull the filter: if you cannot see light through it, that is the problem, or at least the first one. Go outside and look at the condenser: if the fins are packed with grass, fluff or needles, hose them gently from the outside with the power off. Look at the copper line where it enters the unit: if it is iced, switch the system off at the thermostat, run the fan only for a couple of hours to thaw it, and change the filter before switching it back on.

If those are fine, the likely causes are a refrigerant leak, which makes the system cool a little less each week until it stops; a compressor that hums but no longer pumps; or a condenser fan that has stopped, which you can see. All three are technician jobs.

Then there is the Houston case where nothing is broken. A system sized for the house in 1995, now running through leaking attic ducts at 140 degrees on an August afternoon, may simply not be able to hold 72. That is not a repair. It is duct sealing, insulation or a larger system, and an honest contractor will say which, with numbers.